Carbene compounds and organic electroluminescent devices

ABSTRACT

Provided is a compound having Formula I 
     
       
         
         
             
             
         
       
     
     where rings A and B are independently a five-membered or six-membered, carbocyclic or heterocyclic ring, each of which is optionally aromatic; together with nitrogen atoms bonded to ring A and ring B, ring W is a 5-membered N-heterocyclic carbene; and the remaining variables are as defined herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 16/191,604, filed on Nov. 15, 2018, which claims priority under35 U.S.C. § 119(e) to U.S. Provisional Application Nos. 62/725,069 filedAug. 30, 2018; 62/721,299 filed Aug. 22, 2018; 62/652,640 filed Apr. 4,2018; and 62/591,406 filed Nov. 28, 2017; the entire contents of eachare incorporated herein by reference.

GOVERNMENT RIGHTS

This invention was made with government support under Award No.DE-EE0007077 awarded by Office of Energy Efficiency and Renewable Energy(EERE) and United States Department of Energy. The government hascertain rights in the invention.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The invention relates to organic light emitting devices that emit whitelight, and lighting applications of such devices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs. The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative) Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

To our knowledge, the only reported luminescent 2-coordinate Cu(I)compounds are: neutral, 2-coordinate carbene-Cu-amide compoundsdescribed in U.S. Pat. No. 9,853,229, assigned to University of SouthernCalifornia; a cationic bis-lutidine compound which is luminescent onlyat 77K, Simon, J. A., Palke, W. E. & Ford, P. C. Inorganic Chemistry1996, 35, 6413-21; cationic bis-carbene compounds, Shi, S. Y. et al.Dalton Transactions 2017, 46, 745-752, and Gernert, M., et al.,Chemistry A European Journal 2017, 23, 2206-16; neutral carbene-Cuhalides, aryls, acetylides, alkoxides, thiolates, and amides. See,Romanov, A. S. et al. Chemical Communications 2016, 52, 6379-6382,Hamze, R. et al. Chemical Communications 201753, 9008-11, Bochmann, M.et al. Chemistry A European Journal 2017, 23, 4625-37. Additionally, aseries of Cu(I) compounder featuring a sterically-demanding thiolateligand and a monodentate phosphine, lutidine, ether, thioketone, and NHCwere reported in 2008, and did not include any photophysicalcharacterization.

Bochmann and coworkers report the mechanism of luminescence for a2-coordinate carbene-Cu(carbazole) compound. See, Di, D. W. et al.High-performance light-emitting diodes based on carbene-metal-amides.Science 2017, 356, 159-163, and Bochmann, M., et al., WO2017046572. Thegroup reports molecular rotation around carbene-Cu or Cu—N bond, whichin turn allows for spin-inversion and a stabilization of the firstexcited singlet state below the lowest triplet manifold. This process istermed “rotation-assisted spin inversion” (RASI). We propose analternative photopysical mechanism in which there are two triplet statesin equilibrium, one ligand localized and the other charge transfer incharacter. Bochman et al. does not report PLQY or k_(r) of theircompounds. Although Cu(I) compounds have been reported to have k_(r)≥10⁵s⁻¹, the majority of which are dinuclear (CuX)_(n) compounds that makeuse of the additional SOC induced by the halide, X. In contrast, the fewmononuclear Cu(I) compounds with high radiative rates (k_(r)≥10⁵ s⁻¹)also have high non-radiative rates in fluid and polymeric matrices.Bochmann has also reported a vacuum-deposited OLED with CAAC-AuCzcomplex as a dopant. See, Conaghan et al., “Efficient Vacuum-ProcessedLight-Emitting Diodes Based on Carbene-Metal-Amides” Advanced Materials0, 1802285, doi:10.1002/adma.201802285 (2018)

OLED devices based on two-coordinate mononuclear Cu compounds include atwo-coordinate bis-CAAC Cu OLED which showed inefficient energy transferfrom the host to the dopant as well as a CAAC-Cu-Cz OLED which shows anEQE of 9%. Both OLEDs were fabricated through solution process.

SUMMARY

Two-coordinate metal (I)carbene compounds selected from the groupconsisting of Formula I, Formula II, and Formula III,

wherein

ring A, ring B, and ring C are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic;

ring W of Formula I is a 6-membered heterocyclic ring, and ring W ofFormula II or Formula III is a 5-membered or 6-membered heterocyclicring;

L is a monodentate ligand with a metal coordinating member selected fromthe group consisting of C, N, O, S, and P;

M is a metal selected from the group consisting of Cu, Au, and Ag;

R^(A), R^(B), R^(C), and R^(W) represent mono to the maximum allowablesubstitution, or no substitution, and each R^(A), R^(B), and R^(C) isindependently hydrogen or a substituent selected from the groupconsisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, nitrile,isonitrile, sulfanyl, and combinations thereof; or optionally, any twoadjacent R^(A), R^(B), R^(C), or R^(W) can join to form a ring, which isoptionally substituted; and

wherein for the compounds of Formula I, the two R^(W) do not join toform a naphthalene fused to ring W;

wherein the compounds of Formulae II and III do not include a carbeneligand A

ligand A, wherein

ring Q is a five-membered or six-membered ring,

R^(Q), R^(S) and R^(T) are independently selected from the groupconsisting of hydrogen, a C₁₋₂₀ alkyl, and two R^(Q), or R^(S) andR^(T), can join to form an optionally substituted saturated cyclichydrocarbyl ring with an optional heteroatom; and

R^(P) is selected from an optionally substituted alkyl, an optionallysubstituted alkenyl, an optionally substituted aryl, and an optionallysubstituted heteroaryl.

According to another aspect, a compound having Formula I

is disclosed; wherein

ring A and ring B are independently a five-membered or six-membered,carbocyclic or heterocyclic ring, each of which is optionally aromatic;

together with nitrogen atoms bonded to ring A and ring B, ring W is a5-membered N-heterocyclic carbene;

L is a monodentate ligand with a coordinating member selected from thegroup consisting of C, N, O, S, and P;

M is a metal selected from the group consisting of Cu, Au, and Ag;

R^(A), R^(B), and R^(W) represent mono to the maximum allowablesubstitution, or no substitution, and each R^(A) and R^(B) isindependently selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof;

R^(W) is selected from the group consisting of deuterium, fluorine,alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile,sulfanyl, and combinations thereof; or optionally, any two adjacentR^(A), R^(B), or R^(W) can join to form a ring, which is optionallysubstituted; and

two R^(W) do not join to form a naphthalene fused to ring W.

An organic electroluminescent device that includes an anode, a cathode,and an organic layer comprising a compound selected from Formula I,Formula II, or Formula III as defined herein.

A consumer product comprising an organic light-emitting device (OLED),the OLED including an anode, a cathode, and an organic layer comprisinga compound selected from Formula I, Formula II, and Formula III asdefined herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 . shows an organic light emitting device.

FIG. 2 . shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 . Molecular structures of compounds 1 to 5.

FIG. 4 a . The emission spectra of compounds 1 to 5 as 1% polystyrene(PS) films at room temperature (RT) and 77 K.

FIG. 4 b . The natural log of the non-radiative rate plotted against ΔEfor compounds 1 to 5 as 1% polystyrene films at room temperature.

FIG. 5 a . Emission spectra of compound 1 in methylcyclohexane (MeCy) atRT and 77 K.

FIG. 5 b . Emission spectra of compound 2 in MeCy and2-methy-ltetrahydrofuran (MeTHF) at RT and 77 K.

FIG. 5 c . Emission spectra of compound 3 in MeCy and MeTHF at RT and 77K.

FIG. 5 d . Emission spectra of compound 4 in MeCy and MeTHF at RT and 77K.

FIG. 6 . Emission lifetime versus temperature of complex 3.

FIG. 7 . X-ray structures of compounds 6a, 6c, 6d, 7, 8, 9, 10b, and 11.Hydrogen atoms and methyl groups on the Dipp group are removed forclarity.

FIG. 8 . Plot of v_(CT) (in MeCy) versus oxidation energy for compounds6a, 7, 8, 9, in MeCy.

FIG. 9 . Emission spectra of compounds 6a-6d in MeTHF at RT (top) and77K (bottom).

FIG. 10 . Emission spectra of compounds 6a, 7, 8, and 9, in MeTHF at RT(top) and 77K (bottom).

FIG. 11 . Emission spectra of compounds 6a, 7, 8, and 9, as 1% PS filmsat RT (top) and 77K (bottom).

FIG. 12 . Emission in MeTHF at 77K of compound 6a (steady state) and ofpotassium carbazolide (KCz; gated phosphorescence). The decay lifetimesof the compounds are listed.

FIG. 13 a . Temperature-dependent PL decay of compound 6a as 1% PS film.The inset show the parameters obtained from fitting the data to equationin FIG. 13 c.

FIG. 13 b . Temperature-dependent PL decay of compound 9 as 1% PS film.

FIG. 14 . Emission of compound 11 in MeCy at RT and 77K.

FIG. 15 . OLED architecture and the molecular structures of thecompounds used in Device 1 (D1) and Device 2 (D2). D1 includes HATCN ashole-injecting layer (HIL) and NPD as hole-transport layer (HTL). D2 hasthe same layer structure as D1 except no HATCN HIL.

FIG. 16 . Electroluminescent spectra for D1 and D2;

FIG. 17 a . OLED architecture and the molecular structures of thecompounds used in Device 3 (D3).

FIG. 17 b . Electroluminescent spectra of D3;

FIG. 18 a . OLED architecture and the molecular structures of thecompounds used in Device 4 (D4).

FIG. 18 b . Electroluminescent spectra of D4;

FIG. 19 a . OLED architecture and the molecular structures of thecompounds used in Device 5 (D5), Device 6 (D6), and Device 7 (D7), withcompound 3 doped at 10%, 20%, and 40%, by volume, respectively.

FIG. 19 b . Electroluminescent spectra for D5, D6, and D7.

FIG. 20 . External quantum efficiency data data for D5, D6, and D7.

FIG. 21 a . OLED architecture and the molecular structures of thecompounds used in Device 8 (D8), Device 9 (D9), and Device 10 (D10),each doped at 10% by volume of compound 3 in TPBi with a layer thicknessof 30 nm, 40 nm, and 50 nm, respectively.

FIG. 21 b Electroluminescent spectra for D8, D9, and D10.

FIG. 22 Emission spectra of compounds 12a (labeled 4), compound 12c(labeled 6), and compound 12d (labeled 7) in MeCy at room temperature.

FIG. 23 . Emission spectra THF (left), and in MeTHF (right) of compounds12a (spectrum 1), compound 13 (spectrum 2), and compound 14 (spectrum 3)at RT and 77K.

FIG. 24 . Absorption and emission spectra of compound 12 in MeCy (dashedlines) and 2-MeTHF (solid lines) at RT.

FIG. 25 . Emission spectra in THF (left), and in 2-MeTHF (right), ofcompound 9 (spectrum 4), compound 15 (spectrum 5), and compound 16(spectrum 6), at room temperature and 77K.

FIG. 26 . Absorption and emission spectra of compound 11 (spectrum 7),compound 17 (spectrum 8), and compound 18 (spectrum 9) in MeCy at roomtemperature.

FIG. 27 . Emission spectra of compound 3 at room temperature and at 77Kin 2-MeTHF, MeCy, and as 1% PS film.

FIG. 28 . Emission spectra of compound 19 at room temperature and at 77Kin 2-MeTHF, MeCy, and as 1% PS film.

DETAILED DESCRIPTION

We describe a class of luminescent two-coordinate metal(I) carbenecompounds with planar or twisted geometry (i.e., opposite coordinatingring systems out of plane) about the metal. The metal(I) is selectedfrom Cu(I), Ag(I), and Au(I). The compounds can be further described asa combination of a monodentate carbene ligand and a monodentate neutralligand, or a combination of a monodentate carbene ligand and amonodentate monoanionic ligand, to provide two-coordinated metal(I)compounds that have an overall cationic or neutral charge, respectively.An exemplary family of carbenes include the cyclic alkyl amino carbenes(CAACs), as well as conventional and non-conventional N-heterocycliccarbene ligands such as imidazol-2-ylidene (BzI), monoamido-aminocarbene(MAACs), and diamidocarbene (DACs).

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2 .

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2 .For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and organic vaporjet printing (OVJP). Other methods may also be used. The materials to bedeposited may be modified to make them compatible with a particulardeposition method. For example, substituents such as alkyl and arylgroups, branched or unbranched, and preferably containing at least 3carbons, may be used in small molecules to enhance their ability toundergo solution processing. Substituents having 20 carbons or more maybe used, and 3-20 carbons is a preferred range. Materials withasymmetric structures may have better solution processibility than thosehaving symmetric structures, because asymmetric materials may have alower tendency to recrystallize. Dendrimer substituents may be used toenhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. A consumer product comprising an OLED thatincludes the compound of the present disclosure in the organic layer inthe OLED is disclosed. Such consumer products would include any kind ofproducts that include one or more light source(s) and/or one or more ofsome type of visual displays. Some examples of such consumer productsinclude flat panel displays, curved displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, rollable displays, foldabledisplays, stretchable displays, laser printers, telephones, mobilephones, tablets, phablets, personal digital assistants (PDAs), wearabledevices, laptop computers, digital cameras, camcorders, viewfinders,micro-displays (displays that are less than 2 inches diagonal), 3-Ddisplays, virtual reality or augmented reality displays, vehicles, videowalls comprising multiple displays tiled together, theater or stadiumscreen, a light therapy device, and a sign. Various control mechanismsmay be used to control devices fabricated in accordance with the presentinvention, including passive matrix and active matrix. Many of thedevices are intended for use in a temperature range comfortable tohumans, such as 18 degrees C. to 30 degrees C., and more preferably atroom temperature (20-25 degrees C.), but could be used outside thistemperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms “halo,” “halogen,” and “halide” are used interchangeably andrefer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_(S)).

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—R_(S) or—C(O)—O—R_(S)) radical.

The term “ether” refers to an —OR_(S) radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and referto a —SRS radical.

The term “sulfinyl” refers to a —S(O)—R_(S) radical.

The term “sulfonyl” refers to a —SO₂—R_(S) radical.

The term “phosphino” refers to a —P(R_(S))₃ radical, wherein each R canbe same or different.

The term “silyl” refers to a —Si(R_(S))₃ radical, wherein each R_(S) canbe same or different.

In each of the above, R_(S) can be hydrogen or a substituent selectedfrom the group consisting of deuterium, halogen, alkyl, cycloalkyl,heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl,alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, andcombination thereof. Preferred R_(S) is selected from the groupconsisting of alkyl, cycloalkyl, aryl, heteroaryl, and combinationthereof.

The term “alkyl” refers to and includes both straight and branched chainalkyl radicals. Preferred alkyl groups are those containing from one tofifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl,2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, and the like. Additionally, the alkyl group isoptionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, andspiro alkyl radicals. Preferred cycloalkyl groups are those containing 3to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl,cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl,adamantyl, and the like. Additionally, the cycloalkyl group isoptionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or acycloalkyl radical, respectively, having at least one carbon atomreplaced by a heteroatom. Optionally the at least one heteroatom isselected from O, S, N, P, B, Si and Se, preferably, 0, S or N.Additionally, the heteroalkyl or heterocycloalkyl group is optionallysubstituted.

The term “alkenyl” refers to and includes both straight and branchedchain alkene radicals. Alkenyl groups are essentially alkyl groups thatinclude at least one carbon-carbon double bond in the alkyl chain.Cycloalkenyl groups are essentially cycloalkyl groups that include atleast one carbon-carbon double bond in the cycloalkyl ring. The term“heteroalkenyl” as used herein refers to an alkenyl radical having atleast one carbon atom replaced by a heteroatom. Optionally the at leastone heteroatom is selected from O, S, N, P, B, Si, and Se, preferably,O, S, or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups arethose containing two to fifteen carbon atoms. Additionally, the alkenyl,cycloalkenyl, or heteroalkenyl group is optionally substituted.

The term “alkynyl” refers to and includes both straight and branchedchain alkyne radicals. Preferred alkynyl groups are those containing twoto fifteen carbon atoms. Additionally, the alkynyl group is optionallysubstituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer toan alkyl group that is substituted with an aryl group. Additionally, thearalkyl group is optionally substituted.

The term “heterocyclic group” refers to and includes aromatic andnon-aromatic cyclic radicals containing at least one heteroatom.Optionally the at least one heteroatom is selected from O, S, N, P, B,Si, and Se, preferably, O, S, or N. Hetero-aromatic cyclic radicals maybe used interchangeably with heteroaryl. Preferred hetero-non-aromaticcyclic groups are those containing 3 to 7 ring atoms which includes atleast one hetero atom, and includes cyclic amines such as morpholino,piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers,such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and thelike. Additionally, the heterocyclic group may be optionallysubstituted.

The term “aryl” refers to and includes both single-ring aromatichydrocarbyl groups and polycyclic aromatic ring systems. The polycyclicrings may have two or more rings in which two carbons are common to twoadjoining rings (the rings are “fused”) wherein at least one of therings is an aromatic hydrocarbyl group, e.g., the other rings can becycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls.Preferred aryl groups are those containing six to thirty carbon atoms,preferably six to twenty carbon atoms, more preferably six to twelvecarbon atoms. Especially preferred is an aryl group having six carbons,ten carbons or twelve carbons. Suitable aryl groups include phenyl,biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene, preferably phenyl, biphenyl, triphenyl,triphenylene, fluorene, and naphthalene. Additionally, the aryl group isoptionally substituted.

The term “heteroaryl” refers to and includes both single-ring aromaticgroups and polycyclic aromatic ring systems that include at least oneheteroatom. The heteroatoms include, but are not limited to O, S, N, P,B, Si, and Se. In many instances, O, S, or N are the preferredheteroatoms. Hetero-single ring aromatic systems are preferably singlerings with 5 or 6 ring atoms, and the ring can have from one to sixheteroatoms. The hetero-polycyclic ring systems can have two or morerings in which two atoms are common to two adjoining rings (the ringsare “fused”) wherein at least one of the rings is a heteroaryl, e.g.,the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles,and/or heteroaryls. The hetero-polycyclic aromatic ring systems can havefrom one to six heteroatoms per ring of the polycyclic aromatic ringsystem. Preferred heteroaryl groups are those containing three to thirtycarbon atoms, preferably three to twenty carbon atoms, more preferablythree to twelve carbon atoms. Suitable heteroaryl groups includedibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene,benzofuran, benzothiophene, benzoselenophene, carbazole,indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole,triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole,thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine,oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole,indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline,isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine,phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine,phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine,preferably dibenzothiophene, dibenzofuran, dibenzoselenophene,carbazole, indolocarbazole, imidazole, pyridine, triazine,benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine,and aza-analogs thereof. Additionally, the heteroaryl group isoptionally substituted.

Of the aryl and heteroaryl groups listed above, the groups oftriphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran,dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine,pyrazine, pyrimidine, triazine, and benzimidazole, and the respectiveaza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl,and heteroaryl, as used herein, are independently unsubstituted, orindependently substituted, with one or more general substituents.

In many instances, the general substituents are selected from the groupconsisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylicacid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof.

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof.

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy,aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinationsthereof.

In yet other instances, the more preferred general substituents areselected from the group consisting of deuterium, fluorine, alkyl,cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent otherthan H that is bonded to the relevant position, e.g., a carbon ornitrogen. For example, when R′ represents mono-substitution, then one R′must be other than H (i.e., a substitution) Similarly, when R′represents di-substitution, then two of R′ must be other than H.Similarly, when R′ represents no substitution, R′, for example, can be ahydrogen for available valencies of ring atoms, as in carbon atoms forbenzene and the nitrogen atom in pyrrole, or simply represents nothingfor ring atoms with fully filled valencies, e.g., the nitrogen atom inpyridine. The maximum number of substitutions possible in a ringstructure will depend on the total number of available valencies in thering atoms.

As used herein, “combinations thereof” indicates that one or moremembers of the applicable list are combined to form a known orchemically stable arrangement that one of ordinary skill in the art canenvision from the applicable list. For example, an alkyl and deuteriumcan be combined to form a partial or fully deuterated alkyl group; ahalogen and alkyl can be combined to form a halogenated alkylsubstituent; and a halogen, alkyl, and aryl can be combined to form ahalogenated arylalkyl. In one instance, the term substitution includes acombination of two to four of the listed groups. In another instance,the term substitution includes a combination of two to three groups. Inyet another instance, the term substitution includes a combination oftwo groups. Preferred combinations of substituent groups are those thatcontain up to fifty atoms that are not hydrogen or deuterium, or thosewhich include up to forty atoms that are not hydrogen or deuterium, orthose that include up to thirty atoms that are not hydrogen ordeuterium. In many instances, a preferred combination of substituentgroups will include up to twenty atoms that are not hydrogen ordeuterium.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. Oneof ordinary skill in the art can readily envision other nitrogen analogsof the aza-derivatives described above, and all such analogs areintended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuteratedcompounds can be readily prepared using methods known in the art. Forexample, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, andU.S. Pat. Application Pub. No. US 2011/0037057, which are herebyincorporated by reference in their entireties, describe the making ofdeuterium-substituted organometallic complexes. Further reference ismade to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt etal., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which areincorporated by reference in their entireties, describe the deuterationof the methylene hydrogens in benzyl amines and efficient pathways toreplace aromatic ring hydrogens with deuterium, respectively.

As used herein, “electron-withdrawing substituent” refers to anindividual atom, e.g., fluorine, or a functional group that withdrawselectron density from a conjugated ring system, e.g., an aromatic ringsystem. Some examples of electron-withdrawing groups include —F, —CF₃,—NO₂, and ester.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. phenyl, phenylene,naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g.benzene, naphthalene, dibenzofuran). As used herein, these differentways of designating a substituent or attached fragment are considered tobe equivalent.

We describe carbene compounds selected from the group consisting ofFormula I, Formula II, and Formula III,

wherein

ring A, ring B, and ring C are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic;

ring W of Formula I is a 6-membered heterocyclic ring, and ring W ofFormula II or Formula III is a 5-membered or 6-membered heterocyclicring;

L is a monodentate ligand with a metal coordinating member selected fromthe group consisting of C, N, O, S, and P;

M is a metal selected from the group consisting of Cu, Au, and Ag;

R^(A), R^(B), R^(C), and R^(W) represent mono to the maximum allowablesubstitution, or no substitution, and each R^(A), R^(B), and R^(C) isindependently selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof; or optionally, any two adjacent R^(A), R^(B),R^(C), or R^(W) can join to form a ring, which is optionallysubstituted; and

wherein for the compounds of Formula I, the two R^(W) do not join toform a naphthalene fused to ring W;

wherein the compounds of Formulae II and III do not include a carbeneligand A

wherein

ring Q is a five-membered or six-membered ring,

R^(Q), R^(S) and R^(T) are independently selected from the groupconsisting of hydrogen, a C₁₋₂₀ alkyl, and two R^(Q), or R^(S) andR^(T), can join to form an optionally substituted saturated cyclichydrocarbyl ring with an optional heteroatom; and

R^(P) is selected from an optionally substituted alkyl, an optionallysubstituted alkenyl, an optionally substituted aryl, and an optionallysubstituted heteroaryl.

In some instances, R^(A), R^(B), R^(C), and R^(W) are selected from thegroup consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinationsthereof.

In some instances, the R^(A), R^(B), R^(C), and R^(W) are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy,aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinationsthereof.

In yet other instances, a preferred listing of R^(A), R^(B), R^(C), andR^(W) are selected from the group consisting of deuterium, fluorine,alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof.

Luminescent two-coordinate metal(I) carbene compounds that are ofparticular interest will have an overall neutral charge and include amonodentate organoamide ligand, a monodentate alkylide ligand, amonodentate arylide ligand, a monodentate organooxide, or a monodentateorganosulfide ligand. In one embodiment, the compounds are likely tohave a carbene ligand selected from CAAC, BzI, MAAC, or DAC. Theorganoamide, alkylide, arylide, organooxide, or organosulfide ligandwill likely have a core molecular ring structure that is optionallysubstituted, and in many instances the core structure will be anaromatic ring system that includes two or more, e.g., a two to fivefused ring structure, that is substantially planar. In some instances,the amide, oxide, or sulfide ligand will include substituents that crowdor protect the metal center, which is believed to enhance the stabilityof the compound in its ground and/or its electronically excited states.Perhaps, more importantly, the substantially planar ring systems willtend to be twisted out of the plane relative to the ring system of theopposite carbene ligand. The angle of twist out of the plane can be in arange from 30° to as much as 90°, and more likely in a range from 50° to90° or from 65° to 90°.

Some of the exemplary monodentate monoanionic ligands investigatedinclude substituted and non-substituted carbazolides, diphenylamides,substituted phenyl, a substituted phenyl oxide, or a substituted phenylsulfide, as well as the corresponding aza-analogs of each.Representative monodentate neutral ligands include, but not limited to,tertiary amines, N-heteroaryl ligands (e.g., pyridyl, pyrimidine,triazole), phosphines, e.g., triaryl or triaryloxy phosphines. Again,any one of such ligands are likely to be substituted to stericallyenhance the stabilization of the excited state in each metal(I) carbenecompound, and therefore, improve upon corresponding device lifetimes.The compounds can exhibit high quantum efficiency up to 100% in fluidand polymeric matrices with radiative rates on the order of 10⁵ s⁻¹,which are unknown for Cu(I), Ag(I) or Au(I) metal centers. Theseradiative rates are comparable to state of the art known organoiridiumand organoplatinum phosphorescent complexes.

The character of the radiative transition is believed to be chargetransfer from the electron rich monodentate ligand, e.g., an organoamideor alkylide, to the electron-deficient carbene with little metalcentered contribution. The associated charge transfer (CT) state ischaracterized by a high extinction coefficient in absorption (ε˜10³M⁻¹·cm⁻¹). Furthermore, the CT state in question exhibits a small energysplitting between its singlet and triplet manifolds, withΔE_(1CT-3CT)≤150 meV, preferably less than 100 meV, resulting incompounds that resemble highly-efficient thermally activated delayedfluorescence (TADF) compounds. In many instances this singlet andtriplet manifolds (ΔE_(1CT-3CT)) is defined in a range from 10 meV to150 meV, 20 meV to 100 meV, 20 meV to 80 meV, or 30 meV to 60 meV.

For many of the carbene metal(I) amide compounds, and in particular, forthe amide carbazolide compounds described below, we note the presence ofa closely-lying localized triplet state, ³LE, which is amide-centered,e.g., carbazolide-centered. This ³LE can admix with ³CT to varyingdegrees, depending on the solvating matrix as well as on the nature ofthe carbene. Accordingly, emission color (and the related ^(1/3)CT/³LEordering) can be tuned as desired by modulating the electron-acceptingability of the carbene and the electron donating ability of the amide.The design of such compounds can provide for color tuning over 240 nm,i.e., from deep blue/violet, to red, and therefore, cover most, if notall, of the visible spectrum.

The compounds can be used in an organic electroluminescent device aslight-emitting dopants or as non-emitting host materials. For example,as light-emitting dopants the fine tuning of the metal(I) coordinationenvironment can result in a blue emitting dopant, a green emittingdopant, an orange (amber) emitting dopant, or a red emitting dopant. Theterm “red emitting dopant” refers to a compound of the invention with apeak emissive wavelength of from 580 nm to 680 nm, or from 600 nm to 660nm, or from 615 nm to 635 nm. The term “green emitting dopant” refers toa compound of the invention with a peak emissive wavelength of 500 nm to580 nm, or from 510 nm to 550 nm. The term “blue emitting dopant” refersto a compound of the invention with a peak emissive wavelength of from410 nm to 490 nm, or from 430 nm to 480 nm, or from 440 nm to 475 nm.Lastly, the term “amber emitting dopant” refers to a compound of theinvention with a peak emissive wavelength of from 570 nm to 600 nm.

The two-coordinate metal(I) carbene compounds of the invention can be anemissive dopant. In some embodiments, the compound can produce emissionsvia phosphorescence, fluorescence, thermally activated delayedfluorescence, i.e., TADF (also referred to as E-type delayedfluorescence; see, e.g., U.S. application Ser. No. 15/700,352, which ishereby incorporated by reference in its entirety), triplet-tripletannihilation, or combinations of these processes.

It is believed that the internal quantum efficiency (IQE) of fluorescentOLEDs can exceed the 25% spin statistics limit through delayedfluorescence. As used herein, there are two types of delayedfluorescence, i.e. P-type delayed fluorescence and E-type delayedfluorescence. P-type delayed fluorescence is generated fromtriplet-triplet annihilation (TTA).

On the other hand, E-type delayed fluorescence does not rely on thecollision of two triplets, but rather on the thermal population betweenthe triplet states and the singlet excited states. Compounds that arecapable of generating E-type delayed fluorescence are required to havevery small singlet-triplet gaps. Thermal energy can activate thetransition from the triplet state back to the singlet state. This typeof delayed fluorescence is also known as thermally activated delayedfluorescence (TADF). A distinctive feature of TADF is that the delayedcomponent increases as temperature rises due to the increased thermalenergy. If the reverse intersystem crossing rate is fast enough tominimize the non-radiative decay from the triplet state, the fraction ofback populated singlet excited states can potentially reach 75%. Thetotal singlet fraction can be 100%, far exceeding the spin statisticslimit for electrically generated excitons.

E-type delayed fluorescence characteristics can be found in an exciplexsystem or in a single compound. Without being bound by theory, it isbelieved that E-type delayed fluorescence requires the luminescentmaterial to have a small singlet-triplet energy gap (ΔE_(S-T)). Organic,non-metal containing, donor-acceptor luminescent materials may be ableto achieve this. The emission in these materials is often characterizedas a donor-acceptor charge-transfer (CT) type emission. The spatialseparation of the HOMO and LUMO in these donor-acceptor type compoundsoften results in small ΔE_(S-T). These states may involve CT states.Often, donor-acceptor luminescent materials are constructed byconnecting an electron donor moiety such as amino- orcarbazole-derivatives and an electron acceptor moiety such asN-containing six-membered aromatic ring.

As stated, many of the two-coordinate, metal(I) carbene compounds arecharacterized by those of ordinary skill in the art as TADF emitters.Accordingly, the device emits a luminescent radiation at roomtemperature when a voltage is applied across the organic light emittingdevice, and the luminescent radiation comprises a first radiationcomponent. The first radiation component is from a delayed fluorescentprocess or triplet exciton harvesting process. In one embodiment, thelifetime of the first radiation component is at least 1 microsecond.

In another embodiment, the organic emissive layer that includes thecompounds of the invention described above will further include a firstphosphorescent emitting material such that the luminescent radiationcomprises a second radiation component. The second radiation componentarises from the first phosphorescent emitting material. In someinstances, the organic emissive layer further includes a secondphosphorescent emitting material.

In one embodiment, the luminescent radiation is a white light. In someinstances, a first device comprises a second organic light emittingdevice, and the second organic light emitting device is stacked on thefirst device.

In one embodiment, the first radiation component is a blue light with apeak wavelength of about 400 nm to about 500 nm. In another embodiment,the first radiation component is a yellow light with a peak wavelengthof about 530 nm to about 580 nm.

In addition, many of the two-coordinate metal(I) carbene compoundsexhibit remarkably-strong permanent dipoles μD in a range from 4D to24D, e.g., from 8 D to 20 D. In fact, many of the two-coordinatemetal(I) carbene compounds exhibit remarkably-strong permanent dipolesof with μD greater than 11 D (calculated), which gives rise toremarkable solvatochromic properties. Another observed property of thecompounds is their relatively unusual and high thermal stability, whichallows for obtaining the compounds with high purity via sublimation,which provides for the fabrication of vapor-deposited organic layers,e.g., an organic emitting layer, in OLEDs. For example we describe themaking of OLEDs with the compounds (MAAC*)M(I)Cz, (MAAC*) M(I) (CzCN),and (CAAC^(Men)) M(I)Cz as emitter dopants in a host material. Again,M(I) is selected from Cu(I), Ag(I), or Au(I). Many devices exhibitedhigh external quantum efficiency (EQE) up to 10% and a brightness of43,304 cd/m². In addition, the short emission decay lifetime reduces theefficiency roll-off at high driving currents, which addresses a knowntechnical problem in many of the previously reported Cu OLEDs withmononuclear dopants. Blue OLEDs can also be made utilizing a high energy2-coordinate Cu phosphor as a host material, making it the first devicewith an all copper emissive layer, i.e., a copper metal compound as ahost and another copper metal compound as a dopant emitter. The2-coordinate metal(I) carbene phosphor host will tend to have a higher³LE than the 2-coordinate metal(I) emitter dopant.

The 2-coordinate metal(I) carbene compounds have an advantage ofminimizing or avoiding certain modes of excited-state distortion, andthereby allowing for the suppression of non-radiative decay rates(k_(nr)). The 2-coordinate metal(I) compounds also provide anopportunity to structurally modify either side (monodentate ligand) ofthe complexes, which leads to electronic, e.g., the donor-acceptorproperties of the complex, and steric modification, e.g., devicestability. The result is that one can tune the photophysical properties,i.e. emission energies can be tuned throughout visible spectrum andfrontier orbital energies can be tuned for devices. Moreover, selectiveligand modification can provide for charge transport and charge trappingto occur on the ligands themselves with little contribution from themetal. This minimizes large reorganization energies associated with MLCTtransitions in the metal(I) complexes.

In addition, by incorporating select group substitutions on the carbeneor the anionic/neutral ligand with a sterically bulky substituent groupone can design provide a more stericcaly encumbered 2-coordinatemetal(I) complexes. This steric protection of the metal center can leadto an increase in stability of the compound in its electronic excitedstate and the corresponding lifetime stability of fabricated devices.Such coordination geometries can hinder rotation around the C-M/M-Nbonds, thereby allowing for the elucidation of the role of molecularrotation and of the coordination environment on the photophysicalproperties of M(I)-carbene compounds of the invention.

In one embodiment, the 2-coordinate metal(I) compounds have an advantageof highly-luminescent compounds with fast radiative rates in fluid andpolymeric media. The compounds exhibit efficient TADF with smallΔE_(1CT-3CT) (≤150 meV) and large radiative rate constants (k_(r)≥10⁵s⁻¹), which is not common in prior metal(I) TADF emitters. The use ofredox active ligands bridged by the d-orbitals of the metal(I) center isbelieved to provide the above unique photophysical features, andthereby, circumventing the TADF conundrum typical of organic systemswhile minimizing reorganization energies typical of metal(I) systems.

In a particular embodiment, the 2-coordinate Cu(I) compounds have anadvantage of highly-luminescent compounds with fast radiative rates influid and polymeric media. The compounds exhibit efficient TADF withsmall ΔE_(1CT-3CT) (≤150 meV) and large radiative rate constants(k_(r)≥10⁵ s⁻¹), which is not common in prior Cu(I) TADF emitters. Theuse of redox active ligands bridged by the d-orbitals of the Cu(I)center is believed to provide the above unique photophysical features,and thereby, circumventing the TADF conundrum typical of organic systemswhile minimizing reorganization energies typical of Cu(I) systems.

A series of 2-coordinate, neutral Cu(I), Ag(I), and Au(I) compounds havebeen synthesized and characterized, and the photophysical properties ofmany compounds are reported in various media. The results from ourpreliminary temperature-dependent photoluminescent experiments are inagreement with TADF as likely the mechanism of luminescence. Allcomplexes have fast radiative rates and high Φ_(PL) in non-rigid media.As stated, the Ag(I) compounds have sub-microsecond excited statelifetimes. The thermal and photo-stability of all the compounds can beimproved upon by crowding the coordinate environment about the metalsuch as by using relatively bulky substituent groups to block access tothe metal.

In our continued work with 2-coordinate Cu(I) carbene compounds (see,U.S. patent application Ser. No. 14/478,838, filed Sep. 5, 2014) we nowdescribe a series of two-coordinate Cu(I) carbene compounds that alsoinclude amide ligands, e.g., carbazole (Cz) and benzimidazole (BzI) aswell as N-heterocyclic carbene ligands monoamido aminocarbene (MAAC*)and diamidocarbene (DAC*) compounds, see the copper compounds of FIG. 3. Quite unexpectedly, many of these compounds exhibit highly efficientTADF. The compounds are found to exhibit high quantum efficiency up to100% in polystyrene films with short decay lifetimes of less than 20 μs,e.g. from 0.1 μs to 20 μs, from 1 μs to 12 μs, or from 0.5 μs to 6 μs.The radiative rate constants of the compounds are in the order of 10⁵s⁻¹ which are extraordinary for Cu(I) compounds and comparable to thoseefficient phosphorescent emitters with noble metals like Ir and Pt.

We also investigated the analogous 2-coordinate silver, Ag(I), and gold,Au(I), carbene compounds with amide ligands. Of particular interest arethe Ag(I) compounds as these compounds are not only highly luminescentbut also have sub-microsecond radiative lifetimes that take advantage oftriplet excited states. This constitutes an order-of-magnitudeenhancement over the radiative lifetimes of state-of-the-artphosphorescent dopants based on six-coordinate Ir(III) compounds, whichare presently used as visible light emitters in OLEDs and high-endconsumer display products. The sub-microsecond radiative lifetimes forthese compounds is important for mediating second-order quenchingprocesses complicit in device degradation. Moreover, the luminescence ofthese coinage metal complexes can be tuned efficiently over the visiblespectrum; we isolated deep blue, sky blue, green, and yellow emitterswith high photoluminescent quantum yields (PLQY, Φ_(PL)) and highradiative rates.

The compounds of Formula I and Formula III above are of particularinterest as are those compounds of Formula I, II, or III in which ring Bis selected from the group consisting of:

an optionally substituted cycloalkyl with 5 to 10 carbons;

an optionally substituted aryl with 6 to 10 carbons;

an optionally substituted heterocyclic with 3 to 8 carbons and 1 to 3heteroatoms; and

an optionally substituted heteroaryl with 3 to 8 carbons and 1 to 4heteroatoms.

Additional compounds of interest will have ring A and/or ring B as a2,6-disubstituted phenyl or an aza-derivative thereof, wherein Cl of the2,6-disubstituted phenyl group is connected to the nitrogen of the ringW.

In one embodiment, L is an amide of the formula NR^(X)R^(Y), and R^(X)and R^(Y) are independently selected from the group consisting ofhydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,aryl, heteroaryl, and combinations thereof; or optionally, R^(X) andR^(Y), can join to form a five-membered or six-membered, carbocyclic orheterocyclic ring, which is optionally substituted. Given that the amideis a formal −l ligand, the metal(I) carbene compound would be neutral.

In another embodiment, L is a phosphide of the formula PR^(X)R^(Y), andR^(X) and R^(Y) are independently selected from the group consisting ofhydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,aryl, heteroaryl, and combinations thereof; or optionally, R^(X) andR^(Y), can join to form a five-membered or six-membered, carbocyclic orheterocyclic ring, which is optionally substituted. Given that thephosphide is a formal −1 ligand, the metal(I) carbene compound would beneutral.

In another embodiment, L is of the formula CR^(X)R^(Y)R^(Z), and R^(X),R^(Y), and R^(Z) are independently selected from the group consisting ofhydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,aryl, heteroaryl, and combinations thereof; or optionally, R^(X) andR^(Y) can join to form a five-membered or six-membered, carbocyclic orheterocyclic ring, which is optionally substituted. Again, the metal(I)carbene compound would be neutral.

In another embodiment, L is an aryl ring, e.g. phenyl, optionally withone or two heteroatoms, including an optionally substituted phenyl ring.The phenyl ring is optionally substituted, particularly in one or bothof the ortho positions (in relation to the C-M bond). Of particularinterest is where L is selected from the group consisting of benzene,naphthalene, and anthracene, or a heteroaryl ring coordinated to themetal through a ring carbon, the heteroaryl ring selected from pyridine,pyrimidine, pyrazine, or benzo-analogs of each thereof. For example, thearyl ring can also be part of a fused polycyclic ring system, e.g,quinoline. Given that an aryl (Y is C) is a formal −l ligand, themetal(I) carbene compound would be neutral.

In another embodiment, L is an organoxide or an organosulfide of theformula —OR^(X) or —SR^(X), respectively, and R^(X) is defined above. Ofparticular interest is where R^(X) is a substituted aryl or heteroarylring, preferably substitution at one or both of the ortho-positions.Given that an oxide or sulfide is a formal −l ligand, the metal(I)carbene compound would be neutral.

In another embodiment, L is a five-membered or six-membered,heterocyclic ring (Y is O or S), which is optionally substituted. Inthis instance, the metal(I) carbene compound would have an overallcharge of +1.

In another embodiment, L is an amine of the formula NR^(X)R^(Y)R^(Z),and R^(X), R^(Y), and R^(Z) are independently selected from the groupconsisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, aryl, heteroaryl, and combinations thereof; oroptionally, R^(X) and R^(Y) can join to form five-membered orsix-membered, carbocyclic or heterocyclic ring, which is optionallysubstituted. In this instance, the metal(I) carbene compound would havean overall charge of +1.

In another embodiment, L is a phosphine of the formula PR^(X)R^(Y)R^(Z),and R^(X), R^(Y), and R^(Z) are independently selected from the groupconsisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, aryl, heteroaryl, and combinations thereof; oroptionally, R^(X) and R^(Y) can join to form a five-membered orsix-membered, carbocyclic or heterocyclic ring, which is optionallysubstituted. In this instance, the metal(I) carbene compound would havean overall charge of +1.

In another embodiment, L is a N-heterocyclic carbene ligand where Y is acarbene carbon, and forms a five-membered or six-membered heterocyclicring, which is optionally substituted. In this instance, the metal(I)carbene compound would have an overall charge of +1.

In another embodiment, a compound is selected from the group consistingof Formula IA, Formula IB, and Formula IC

wherein

L is as defined above;

T is selected from O, S, CR^(m)R^(n), SiR^(m)R^(n), or GeR^(m)R^(n); and

R^(i), R^(j), R^(k), R^(l), R^(m), and R^(n) are independently selectedfrom the group consisting of hydrogen, deuterium, halogen, alkyl,cycloalkyl, heteroalkyl, arylalkyl, amino, silyl, aryl, heteroaryl, andcombinations thereof; or optionally, any two R^(i), R^(j), R^(k), andR^(l), and any two adjacent R^(m) and R^(n), can join to form a ring,which is optionally substituted. In many instances, T is selected from Oor CR^(m)R^(n). Rings A and B as well as R^(A), R^(B), and R^(W), are asdefined above.

In many instances, R^(i), R^(j), R^(k), R^(l), R^(m), and R^(n) areindependently selected from the group consisting of hydrogen, deuterium,alkyl, cycloalkyl, heteroalkyl, aryl, heteroaryl, and combinationsthereof; or optionally, R^(i) joins with R^(j) to form a ring, or twoR^(W) join to form a ring, each of which is optionally substituted.

In another embodiment, we describe metal (I) carbene compounds ofFormula I N, Formula II N, or Formula III N below.

wherein

ring A, ring B, and ring C are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic;

ring W of Formula I is a 6-membered heterocyclic ring, and ring W ofFormula II N or Formula III N is a 5-membered or 6-membered heterocyclicring;

M is a metal selected from the group consisting of Cu, Au, and Ag;

R^(A), R^(B), R^(C), and R^(W) represent mono to the maximum allowablesubstitution, or no substitution, and each R^(A), R^(B), and R^(C) isindependently selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof; or optionally, any two R^(A), R^(B), R^(C), andR^(W) can join to form a ring, which is optionally substituted; and

R¹, R², R^(X), and R^(Y) are independently selected from the groupconsisting of hydrogen, deuterium, fluorine, alkyl, cycloalkyl,cycloalkenyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryl, andcombinations thereof; each of which is optionally substituted;

or optionally, R^(X) and R^(X), can join to form a ring, which isoptionally substituted;

wherein for the compounds of Formula I N, the two R^(W) do not join toform a naphthalene fused to ring W;

wherein the compounds of Formulae II N and III N do not include acarbene ligand A

wherein

ring Q is a five-membered or six-membered ring,

R^(Q), R^(S) and R^(T) are independently selected from the groupconsisting of hydrogen, a C₁₋₂₀ alkyl, and two R^(Q), or R^(S) andR^(T), can join to form an optionally substituted saturated cyclichydrocarbyl ring with an optional heteroatom; and

R^(P) is selected from an optionally substituted alkyl, an optionallysubstituted alkenyl, an optionally substituted aryl, and an optionallysubstituted heteroaryl.

The compounds of Formula I N and Formula III N are of particularinterest as are those compounds in which ring B is selected from thegroup consisting of:

an optionally substituted cycloalkyl with 5 to 10 carbons;

an optionally substituted aryl with 6 to 10 carbons;

an optionally substituted heterocyclic with 3 to 8 carbons and 1 to 3heteroatoms; and

an optionally substituted heteroaryl with 3 to 8 carbons and 1 to 4heteroatoms.

Additional compounds of interest will have ring A and/or ring B as a2,6-disubstituted phenyl or an aza-derivative thereof, wherein Cl of the2,6-disubstituted phenyl group is connected to the nitrogen of the ringW.

The compounds selected from the group consisting of Formula I N1,Formula I N2, and Formula I N3 are of interest.

wherein

T is selected from O, S, CR^(m)R^(n), SiR^(m)R^(n), or GeR^(m)R^(n); and

R^(i), R^(j), R^(k), R^(l), R^(m), and R^(n) are independently selectedfrom the group consisting of hydrogen, deuterium, halogen, alkyl,cycloalkyl, heteroalkyl, arylalkyl, amino, silyl, aryl, heteroaryl, andcombinations thereof; or optionally, any two R^(i), R^(j), R^(k), andR^(l), and any two adjacent R^(m) and R^(n), can join to form a ring,which is optionally substituted. In many instances, T is selected from 0or CR^(m)R^(n). Rings A and B as well as R^(A), R^(B), R^(X), R^(Y), andR^(W) are as defined above.

In many instances, R^(i), R^(j), R^(k), R^(l), R^(m), and R^(n) areindependently selected from the group consisting of hydrogen, deuterium,alkyl, cycloalkyl, heteroalkyl, aryl, heteroaryl, and combinationsthereof; or optionally, R^(i) joins with R to form a ring, or two R^(W)join to form a ring, each of which is optionally substituted.

In many instances, for any compounds structurally defined above, L isNR^(X)R^(Y) is selected from the group consisting of:

an optionally substituted carbazoyl, or an aza-derivative thereof;

an optionally substituted diphenylamino, or an aza-derivative thereof;

wherein R^(x′), R^(y′), and RN are independently selected from the groupconsisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl,heteroalkyl, arylalkyl, amino, silyl, aryl, heteroaryl, and combinationsthereof; and R^(k) and R^(l) are as defined above.

We also describe an OLED that includes an anode, a cathode, and anorganic layer comprising an organic layer, the organic layer comprisinga metal(I)-carbene compound of Formula I, Formula II, or Formula IIIdefined above. In another embodiment, we describe an OLED that includesan anode, a cathode, and an organic layer comprising an organic layer,the organic layer comprising a metal(I)-carbene compound of Formula IA,Formula IB, or Formula IC defined above.

In another embodiment, we describe an OLED that includes an anode, acathode, and an organic layer comprising an organic layer, the organiclayer comprising a metal(I)-carbene compound of Formula I N1, Formula IIN, or Formula III N defined above. In another embodiment, we describe anOLED that includes an anode, a cathode, and an organic layer comprisingan organic layer, the organic layer comprising a metal(I)-carbenecompound of Formula I N1, Formula I N2, or Formula I N3 defined above.

In one embodiment, we describe two-coordinate, neutral Cu(I) carbenecompounds (see, FIG. 3 , and below for quick reference) of(MAAC*)Cu(CzCN₂) (1), (MAAC*)Cu(CzCN) (2), (MAAC*)CuCz (3),(DAC*)Cu(CzCN) (4) and (DAC*)CuCz (5) (* represents isopropylsubstitution of the phenyl groups on N atoms of the carbene ligands, asshown). The incorporation of carbonyls into the cyclic carbene ligand,e.g., the MAACs and DACs, provides a gradual lowering of the LUMO energyconcomitant with an increase in π-accepting properties. The isopropylgroups on the carbene ligands seem to provide enough steric hindrance tominimize the distortion of the compounds in the excited state. Moreover,the compounds are thermally stable, and therefore can be purified bysublimation. Also, the relatively high thermal stability allows thecompounds to be vapor deposited with an emitter host material to form anemitter layer of an OLED. Accordingly, we also describe OLEDs with(MAAC*)CuCz, (MAAC*)Cu(CzCN) and (CAAC^(Men))CuCz as emitter dopantsthat are made using vapor deposition. Each compound exhibits highexternal quantum efficiency (EQE), e.g., up to 10%, with no outcouplingdesign structures. In addition, the short emission decay lifetimereduces the efficiency roll-off at high driving currents, yielding amaximum brightness that can reach or exceed 43,300 cd/m².

Photophysical Properties

Absorption and emission spectra. Molar absorptivity of compounds 1 to 5in MeTHF exhibit strong and broad spin-allowed charge-transfer (CT)transitions, and which are red-shifted from 1 to 4. Vibronic absorptionis observed at ca. 360 nm for all compounds, which is consistent withthe absorption of cabazolide (Cz). For compounds 1 and 2, the CT bandsand the Cz absorption overlap with each other, whereas the CT bands ofcompounds 3 and 4 are lower energy than the Cz bands. The extinctioncoefficients of the CT absorption bands of all compounds are between4000-6000 M⁻¹ cm⁻¹.

Emission spectra of compounds 1 to 5 in 1% polystyrene films are shownin FIG. 4 a . Photophysical data for compounds 1 to 6 in different mediaand as a neat solid are summarized in Table 1. As shown, the emissioncolor changes from deep blue to red from compounds 1 to 5. Collectively,the quantum efficiency at room temperature ranges from 2% to 100% withextremely short decay lifetimes of about 1 μs, i.e. the data lists decaylifetimes from 0.052 to 2.3 μs. In compounds 2 to 5, the emissionspectra are broad and featureless (relative to compound 1) at both roomtemperature (RT) and 77 K, which is indicative of emission from CTstates. Moreover, the emission spectra of compounds 2 to 4 show littleor no shift (differences in position and shape) from RT to 77 K and thelifetimes increase by 2 to 5 orders of magnitude. Accordingly, theluminescence of compounds 2 to 5 is best described asthermally-activated-delayed fluorescence (TADF), which occurs when thehigher lying singlet S₁ is thermally populated from the lowest tripletT₁. This thermal activation requires small energy separation between S₁and T₁, and that explains the small shift or differences between theemission spectra at the different temperatures. The radiative rateconstants of compounds 2 to 4 are in the order of 10⁵ s⁻¹ which arecomparable to those of efficient phosphorescent emitters with noblemetals such as Ir(III) and Pt(II). The non-radiative rate constantsincrease as the emission is red-shifted most likely due to energy gaplaw.

For compound 1, the emission is featureless at RT, though it iswell-resolved and shows a characteristic vibrational structure ofcarbazolide at 77 K. Moreover, the onset of the emission spectrum at RTis blue-shifted relative to 77 K, and the lifetime increases from a fewmicroseconds at RT to 3.2 ms at 77 K. The vibronic spectrum along withthe long lifetime at 77 K is indicative of emission from underlyingtriplet locally-excited (³Cz) state. As temperature increases, internalconversion (IC) from the ³Cz state to ³CT state occurs, followed byup-conversion intersystem crossing (ISC) from the ³CT state to the ¹CTstate. Accordingly, both IC and ISC processes determine the overalldecay rate, and this explains the relatively long lifetime of compound 1at RT compared to that of compounds 2 to 4. A plot of ln(k) against ΔEis plotted, where ΔE is the energy separation between the lowest singletexcited state and the ground state obtained from the emission peak atRT, see FIG. 4 b . For a series of materials which have similar groundand excited states but with varying energy of the excited state, alinear relationship is seen between the log of the non-radiative rateconstant and the energy gap of the transition. As shown, a good linearfit is obtained for compounds 2 to 5. but not for compound 1.

The emission spectra of compounds 1, 2, 3, and 4 at both RT and 77 K areshown in FIGS. 5 a, 5 b, 5 c, and 5 d , respectively (solvent matrix asindicated). For each compound the emission spectra is blue-shifted uponcooling in fluid solvents like MeTHF and methylcyclohexane (MeCy)resulting from destabilization of the CT states in more rigidenvironment. The shift is greater in methylTHF, which is likelyattributed to its greater polarity than methylcyclohexane. The effect isminimized in polystyrene films due to the more rigid solutionenvironment. Due to the relative positions of the ³CT and ³Cz states,each compound behaves differently at lower temperature. Compound 1 showsvibronic emission from the lower lying ³Cz state at 77 K in bothpolystyrene films and methylTHF because thermal activation from thelower lying ³Cz to the ³CT states is hindered. The decay lifetime at 430nm are in the range of milliseconds. The same phenomenon is observed forcompound 2 in MeTHF. However, for compound 2 the ³CT and ³Cz states areclose in methylcyclohexane, and hence a combination of ³Cz and ³CTemission at 77 K is observed with CT dominating the emission. Forcompound 3, which has the CT states lower than the ³LE state, a strongcombination of ³Cz and ³CT emission is only observed in methylTHF at77K, whereas only broad CT emission is shown in methylcyclohexane.Compound 4 shows broad CT emission in all matrices at 77 K that islikely due to the significant lower energy of the CT states than ³Czstate. DFT calculations further prove this rationale (see next section).

TABLE 1 Luminescent properties of complexes 1-6 in different media. τ,_(RT) k_(r, RT) k_(nr, RT) τ, _(77K) Complex λ_(max, RT) Φ_(RT) (μs) 10⁵s⁻¹ 10⁵ s⁻¹ λ_(max, 77K) (μs) solution in 2-MeTHF 1 448 0.24 2.3 1.0 3.3424 9300 2 492 1.00 1.2 8.3 <0.083 428 2200 3 542 0.55 1.1 5.0 4.1 432430 nm: 2100 (62%)  342 (38%) 520 nm: 181 4 602 0.05 0.080 6.2 119 49218 5 666 0.02 0.052 3.8 180 536 213 1 wt % in polystyrene film 1 4320.80  2.6 (47%) 0.9^(a) 0.23^(a) 424 3200 2 468 1.00 1.3 7.7 <0.077 46499 3 506 0.90 1.4 6.4 0.71 502 227 4 548 0.78 1.2 6.5 1.8 544 153 5 6160.30 0.75 4.0 9.3 612 408 6 704 0.03 0.19 1.6 51 682 146 neat solid 1438 0.05 0.37 (33%) 0.38^(a) 7.2^(a) 438 7100 2 474 0.76 0.75 10.0 3.2468 91 3 492 0.53 0.84 6.3 5.5 482 164 4 550 0.68 1.0 6.8 3.2 558 280 5616 0.15 0.33 4.5 26 598 180 6 658 0.12 0.39 3.1 22 634 306^(a)Calculated from weighted average of the two contributions to τ.

The radiative rate constants of the Cu(I) carbene-amide compounds are asfast as those of phosphorescent emitters with heavy metal like Ir andPt. The energy separation between the lowest excited singlet and tripletstates needs to be small to obtain a short radiative TADF decaylifetime, which is important to maximize the photoluminescent quantumefficiency. The emission spectra of compounds 2-5 at 77 K are barelyshifted from those at RT which is also indicative of the small energyseparation between the lowest triplet and singlet state. Therefore, itis of vital importance to measure ΔE(S₁−T₁) of these Cu compounds bytemperature-dependent measurement. FIG. 6 plots emission lifetime ofcompound 3 at different temperatures. ΔE(S₁−T₁) is obtained by fittingthe temperature dependent lifetime measurements to the Arrheniusequation. The activation energy, or ΔE(S₁−T₁), is calculated to be 31.7meV (256 cm⁻¹) for compound 3, which is smaller than the upper limit(130 meV) of ΔE(S₁−T₁) for fast up-intersystem crossing from ³CT to ¹CTstates to occur. In fact, many of the carbene-Cu(I) amide compounds willhave a ΔE(S₁−T₁) in a range from 10 meV to 150 meV, 20 meV to 120 meV,or 20 meV to 80 meV, which again, tells us that the compounds are verypromising TADF emitters.

To obtain parameters governing the temperature dependent luminescentproperties, the emission lifetime of complex 3 in PS film was measuredbetween 5 K and 320 K. The lifetime steadily increases upon coolinguntil near 150 K, where the increase becomes more pronounced, until 50 Kwhere the rate of increase slows. The increase in lifetime at lowtemperature is attributed to successive depopulation of states at highenergy that have radiative rate constants faster than the lowest lyingstate. At temperatures above 50 K, the emission is dominated by ahigher-lying S, state, whose rate of thermal population increases withheating. At temperatures below 50 K, thermal activation between tripletsubstrates is observed. Under an assumption of a fast thermalizationbetween states, the temperature dependent decay curve can be fit to theBoltzmann distribution equation (equation 1).

$\begin{matrix}{\tau = \frac{2 + e^{- \frac{\Delta{E({{III} - I})}}{k_{B}T}} + e^{- \frac{\Delta{E({S_{1} - I})}}{k_{B}T}}}{{2\left( \frac{1}{\tau_{I,{II}}} \right)} + {\left( \frac{1}{\tau_{III}} \right)e^{- \frac{\Delta{E({{III} - I})}}{k_{B}T}}} + {\left( \frac{1}{\tau_{S_{1}}} \right)e^{- \frac{\Delta{E({S_{1} - I})}}{k_{B}T}}}}} & (1)\end{matrix}$

Here, 5, represents the lowest singlet state, whereas I, II and IIIrepresent the triplet substrates ^(I)T₁, ^(II)T₁ and ^(III)T₁, and k_(B)is the Boltzmann constant. Substrates I and II are treated as beingdegenerate since the energy splitting between these two states arenormally very small (<10 cm⁻¹) in copper complexes. Fits of theexperimental lifetime data to equation 1 reveal the decay rate of eachstate and the energy separation between them. Fits are poor to aBoltzmann equation that does not include a second term to account forsplitting of the triplet substrates and plateau at T<50 K. The exchangeenergy is characterized by ΔE(S₁−^(III)T₁), which is determined to be415 cm⁻¹ (51.5 meV). This energy separation is among the smallest valuesreported for Cu-based TADF emitters. The decay lifetime of the S₁ state(τ_(S) ₁ =73.4 ns) is among the fastest values of τ_(S) ₁ for Cucomplexes and consistent with the high k_(r) as mentioned above. Thedecay lifetimes for the ^(III)T₁ and ^(I)T₁/^(II)T₁ substrates are 58.2μs and 206 μs, respectively. The zero-field splitting (ZFS), whichcorresponds to ΔE(III-II/I), is 74 cm⁻¹. The ZFS in compound 3, inducedby the effective spin orbit coupling (SOC) with the metal center, isexceptionally large for a Cu(I) complex.

The values obtained for k_(r)(S₁−S₀), ΔE(S₁−^(III)T₁) and ZFS from thetemperature dependence analysis of compound 3 are unique in comparisonto data reported for luminescent four-coordinate Cu(I) complexes. Incompound 3, k_(r)(S₁−S₀) is large and ΔE(S₁−^(III)T₁) is small relativeto values reported for other Cu(I) lumiphores. The deviation of compound3 from trends in other Cu(I) emitters is likely due to two factors; thelinear, coplanar arrangement of ligands and the minimal, but essential,participation of metal center to the ¹ICT transition. The geometry ofthe complex maximizes π-overlap between the 2p_(z) orbitals on theC_(NHC) and N_(Cz) atoms ligated to Cu, and the highly polarizable 3dorbitals of the metal provide enough electron density to impart highoscillator strength to the ¹ICT transition. On the other hand, overlapbetween the HOMO and LUMO remains poor enough to minimize stabilizationof the unpaired electrons in the 3ICT state, thereby minimizing theexchange energy.

We also fabricated vapor-deposited OLED devices with a neat emitterlayer of compound 3. The device demonstrated both high EQE and lowefficiency roll-off at high voltage, qualities attributed to the highquantum efficiency and the short exciton decay time of these efficientcopper-based emitters. The high EQE of the host-free devicesdemonstrates the potential of the metal(I) carbene compounds used asneat emitters in OLED devices.

Each of compounds 6a, 6c, 6d, 7, 8, 9, and 11 (see, FIG. 7 ) exhibitlinear coordination around the Cu center with the carbene andcarbazolide ligands arranged in a coplanar conformation, with theexception of compound 10b in which the carbene and the carbazole planesare orthogonal to each other.

Compounds 6a, 8, and 9 each include the same carbene ligand but thedonor strength of the carbazolide ligand is increased in the order of 6,8, and 9. The result is an increasingly-stabilized CT band in compound9. The CT band of compound 9 exhibits negative solvatochromism and issubsequently more red-shifted in non-polar solvents such as MeCy. Thedependence of the energy of the CT transition on the donating strengthof the amide is linear, as shown in FIG. 8 , further establishing theredox active nature of the ligands and the CT nature of the lowestenergy transition in these complexes. In contrast, the absorptionspectrum of compound 7, which has a relatively electron-deficient amide(—CN substitution), does not exhibit a distinct CT band in either THF orMeCy, which indicates that the lowest energy transition in compound 7 islikely not CT-dominant in nature. An increase in the steric bulk of thecarbene appears to have little if any effect on the energies orextinctions of the major transitions. However, an increase in stericbulk around the carbazolide ligand, which forces the ligands into anorthogonal conformation as in compound 10, appears to decrease theextinction coefficient of the CT transition.

Room temperature emission spectra of the compounds 6a, 6b. 6c, and 6dwith increasing steric bulk for the carbene ligand CAAC in 2-MeTHF isshown FIG. 9 (top). The emission spectra for each compound is broad andfeatureless and exhibits very little differentiation, which again, isindicative of the CT nature of the radiative transition. The bulkiercompounds, however, exhibit increasing photoluminescent quantum yields(PLQY, Φ_(PL)) and suppressed non-radiative decay rates (see, Table 2),with the most encumbered compound 6a having a remarkable Φ_(PL)=100% andk_(r)=3.9×10⁵ s⁻¹. In frozen 2-MeTHF matrices at 77K, the emission ofcompounds 6a-d becomes narrow and highly structured, with lifetimes onthe order of ms, see, FIG. 9 (bottom). This is consistent with emissionout of a localized excited state (³LE), which is in fact theclosely-lying carbazolide triplet state, ³Cz.

On can functionalize the carbazole ligand with electron-withdrawing(compound 7) and electron-donating (compound 8) groups to provide anemissive blue-shift and a red-shift, respectively, FIG. 10 . Compound 9with the strongest electron-donating diphenylamide exhibits thelowest-energy emission in all solvents and an enhanced DPL in PS due tosuppression of modes of non-radiative deactivation in the more rigidmatrix. Compound 8 exhibits broad and featureless CT emission in2-MeTHF, MeCy, and PS films. Compound 7 exhibits narrower emissionspectra in all matrices, with weak vibronic structure at high energies.This observation is consistent with the absorption spectra of compound 7which shows that the CT transition is not in fact the lowest-energytransition. The CT/³LE manifolds can indeed be weakly admixed, where thelowest-energy adiabatic state in compound 7 is largely ³Cz in character.This is further corroborated by the ms lifetime of the emissive state incompound 7 in PS (Table 2). We also note the peak appearing at lowerenergy in emission spectra of 7 in MeCy and 2-MeTHF, which disappears inPS. This peak is characterized by concentration-dependent emissionintensity as well as a rise time in PL decay. All these observationsallow us to assign the low-energy emission from compound 7 in fluidmedia to excimer formation, which is suppressed in the more rigid PSmatrix.

³Cz-based emission in compounds 6a, 7, and 8 is indicated by thelong-lived decay times and the vibronically-structured spectral lines asobserved in frozen 2-MeTHF and MeCy at 77K, FIG. 11 . This is likely dueto rigidochromic effects destabilizing the low-lying CT bands in 6a and8, such that the lowest lying state at 77K is in fact largely ³Cz innature, FIG. 12 . Compound 9, in contrast, shows broad and featurelessemission at 77K in frozen MeCy and 2-MeTHF, as well as PS films, withlifetimes ˜200 μs. This can be attributed to the CT-³LE gap in compound9 being greater than in the carbazolide compounds owing to its morestrongly-donating amide that gives a more stabilized CT state and a ³LEwith higher energy than ³Cz. Similarly, in a PS film, compound 6aappears to retain its CT emission at low temperatures, with a lifetimeof 64 μs at 77K.

The increase in the decay times observed in compounds 6a and 9 uponcooling is consistent with TADF. Temperature-dependent studies of PSfilms show the characteristic TADF curve, which can be fitted toequation (2) below.

$\begin{matrix}{\tau = \frac{3 + e^{- \frac{\Delta E}{kT}}}{{3\left( \frac{1}{\tau_{1}} \right)} + {\left( \frac{1}{\tau_{2}} \right)e^{- \frac{\Delta E}{kT}}}}} & (2)\end{matrix}$

An Arrhenius analysis allows us to extract the value of ΔE_(1CT-3CT),which is found to be exceedingly small in both compounds: 63 meV (410cm⁻¹) in 6a and 71 meV (570 cm⁻¹) in 9—among the smallest energysplittings in Cu(I)-based TADF compounds. See, FIGS. 13 a and 13 b ,respectively.

Electroluminescence.

Compared to compounds 6a, 8, 9, and 10, compound 11 shows a narrower,more structured emission profile in MeCy at RT, FIG. 14 . However, theradiative rate constant of compound 11 (k_(r)=3.3×10⁵ s⁻¹) is too highto be attributed to a purely ³Cz-centered transition. In contrast, thenarrow emission line shape coupled with the fast radiative rate isbelieved to be an emission out of an adiabatic state comprised of anadmixture of CT and ³Cz. At 77K, emission of compound 11 resembles theCAAC-Cu-amide compounds as it exhibits a very narrow and a lifetime inmilliseconds.

To date, there are only a few reports of Cu(I) compounds that are usedin emitter layers of OLEDs and which are prepared by vapor deposition.One reason has to do with their relatively poor thermal stability, andtherefore, the prior Cu(I) compounds degrade appreciably at theirrespective sublimation temperatures. This is especially true formononuclear Cu(I) compounds. The only reported OLED devices based ontwo-coordinate mononuclear Cu compounds are a two-coordinate bis-CAAC CuOLEDs, which demonstrated inefficient energy transfer from the host tothe dopant. CAAC-Cu-Cz OLED (6b) exhibited an EQE of 9%, and in eachcase, the emitting layers were prepared by solution processing, e.g.,spin coating.

TABLE 2 Photophysical properties of compounds 6a-11 in 1% polystyrenefilms, 2-MeTHF and MeCy. λ_(max, RT) τ_(RT) k_(r, RT) k_(nr, RT)λ_(max, 77K) τ_(77K) Matrix (nm) Φ_(RT) (μs) (10⁵ s⁻¹) (10⁵ s⁻¹) (nm)(ms)  6a 2-MeTHF 492 0.98 2.5 3.9 0.08 430 7.3 MeCy 468, 486 0.92 2.34.0 0.35 430 6.7 PS 474 1.0 2.8 3.5 — 480 0.064  6b 2-MeTHF 510 0.68 2.33.0 1.4 430  3.0 (at 430 nm) 0.05 (at 550 nm)  6c 2-MeTHF 500 0.56 1.83.1 2.4 430 8.7  6d 2-MeTHF 510 0.11 0.54 2.0 16 430 5.02  7 MeCy 428(mono), 0.19 450 nm: 5.9 — — 424 4.3 588 (excim) 600 nm: 2.3 (−7%); 20.5(107%) PS 426 0.82  240 (70%) 0.015 0.0032 424 6.9 1300 (30%)  8 2-MeTHF558 0.25 0.28 8.9 27 470 seconds MeCy 542 0.62 1.1 5.5 3.4 472 secondsPS 578 1.0 2.3 4.3 — 490 0.55  9 2-MeTHF 580 0.16 0.87 1.8 97 498 0.22MeCy 556 0.55 2.4 2.3 1.9 530 0.19 PS 532 0.78 2.6 3.0 0.85 536 0.26 11MeCy 428 0.42 1.3 3.3 4.6 428 6.3

Photophysical and Electroluminescence Data of Compounds 12a, 13, and 14.

Absorption spectra of the CAAC^(Men) M(I)(Cz)compounds 12a, 13, and 14,of Cu(I), Ag(I), and Au(I), respectively, show high energy, sharp peakscorresponding to carbazole-centered transitions (λ<370 nm) that arelargely unchanged regardless of the metal bonded to the amide. Thereare, however, more pronounced differences in the low-lying absorptionbands assigned to charge transfer (CT) transitions. Compound 13 has theweakest ECT, followed by compound 12a, and compound 14. This can beexplained in-part by the obtained X-ray crystal structures of each ofthe compounds. Compound 13 has the longest carbene to amide distance,which corresponds to the least overlap between the frontier molecularorbitals, and consequently the weakest HOMO to LUMO allowed transition.The gold complex (3), having the heaviest metal, exhibits chargetransfer with the strongest allowed transition.

Emission spectra at room temperature (RT) of the compounds 12a, 13, and14 are all broad and featureless, which can be indicative of the CTnature of the transitions. The trend in the energies of the emissionmaxima follows the magnitude of the Stokes shift between absorption andemission, and can be related to the extent of reorganization the complexundergoes when transitioning between the ground and excited states: withthe silver compound 13, having the longest carbene-amide distance andthe smallest HOMO-LUMO overlap, exhibits the largest Stokes shiftbetween absorption and emission, and the most red-shifted emissionλ_(max). The gold compound 14, with its intermediate carbene-amidedistance follows the trend as well, and lastly is the copper compound 12with the shortest carbene-amide separation, the smallest Stokes shift,and the highest energy of emission λ_(max).

At room temperature, all compounds show remarkably-highphotoluminescence quantum yields (Φ_(PL)) in MeCy, with 1.0, 0.71, and0.95 for compounds 12a, 13, and 14, respectively. The excited statelifetime of compound 14 is greater than that of compound 12a owing tothe heavier gold atom, which results in stronger spin-orbit coupling andmore efficient inter-system crossing (ISC). Interestingly, the silvercompound 13 shows the fastest radiative rate of all three compounds,with k_(r)=2×10⁶ s⁻¹ which to our knowledge makes the Ag(I) compound themost efficient Ag(I)-based emitter in fluid medium to date.Non-radiative mechanisms are suppressed in a non-coordinating solventsuch as MeCy allowing compound 13 to demonstrate 100% efficientluminescence while maintaining sub-microsecond radiative lifetime. Tothe best of our knowledge, compound 13 is the first reportedorganometallic complex with Φ_(PL)=100% and a sub-microsecond radiativelifetime. Compound 14 exhibits a Φ_(PL)=95%, to the best of ourknowledge the most efficient Au(I)-based phosphor to date. At 77K,emission spectra of all three compounds exhibit narrow and structuredbands, and with respective lifetimes orders of magnitude longer thanwhat is observed at room temperature. These two observations indicatethat emission at room temperature likely stems from the closely-lyingcarbazolide-centered triplet (³LE), accessible in frozen media due tothe rigidochromic destabilization of the CT state. The gold compound 14bearing the heaviest metal, exhibits the strongest heavy atom effect,and hence displays the fastest ³LE phosphorescence among all threecompounds. Compound 13 on the other hand, with the largest ligandseparation, shows the least metal contribution to the ³LE, and exhibitsweakly-allowed phosphorescence (22 ms).

Relative to the parent compound 12a, the more electron-rich compound 12dshows a red-shift in emission, and the more electron-deficient compound12c shows a blue-shift. Accordingly, substitution of the carbazole withdonating methoxy groups stabilizes the CT state, whereaselectron-withdrawing cyano-groups have a destabilizing effect.Nevertheless, all three complexes still exhibit ligand-centered emissionin frozen media, which suggests that this localized state is notperturbed largely by electronic modification of the carbazole amideligand. To perturb the ligand-centered state away from the CT manifold,non-carbazole amides with triplet energies drastically higher than thatof carbazole can be used.

Photophysical and Electroluminescence Data of Compounds 9, 15, and 16.

Absorption spectra of the corresponding CAAC^(Men) M(I)(NPh₂) compounds9, 15, and 16, M is (Cu(I), Ag(I), and Au(I), respectively, follow thesame trends in the intensity of each respective low-lying CT state. Goldcompound 16 containing the heaviest metal exhibits CT with the highest ε(5.7×10³ M⁻¹·cm⁻¹), and the silver compound 15 has the mostweakly-absorbing CT state. The gold compound 16 appears to be the morestable compound to ambient conditions (moisture or oxygen) in solution.

Room temperature emission spectra of compounds 9, 15, and 16 are allbroad and featureless, and display considerable red-shifts compared totheir carbazole-analogues compounds 12, 13, and 14. Moreover, thedestabilized ³LE state in the compounds appears to impact the radiativerates following Fermi's Golden Rule, and the presence of a high densityof resonant states increases the likelihood of an electronic transitionbetween them. At 77K, the emission remains broad and featureless, anddisplays a marked blue-shift in energy. This observation is indicativeof strong rigidochromic effects with remarkably strong ground andexcited state dipoles. The longer lifetimes upon freezing are likely dueto thermally-activated delayed fluorescence (TADF) operating within theCT manifold.

Photophysical and Electroluminescence Data of Compounds 11, 17, and 18.

Absorption spectra of the benzoimidazole M(I)(Cz)compounds 11, 17, and18, M is Cu(I), Ag(I), and Au(I), respectively, in MeCy exhibit both thesharp, high-energy peaks corresponding to ligand-centered transitions aswell as low-lying broad bands assigned to CT transitions. As with theCu/Ag/Au series above, the most intensely-absorbing CT band is that ofthe gold compound 19, and the most weakly-absorbing CT is that of thesilver compound 17.

Room temperature emission spectra of compounds 11, 17, and 18 in MeCyare narrow and structured, appearing to have more ³LE character, unlikewhat we report for compounds 12-14, 9, 15 and 16 above. The goldcompound 18 is the most efficient phosphor of the series, followed bythe silver compound 17. The lower radiative rate recorded for compound17 compared to its CAAC-analogue, compound 13, could be attributed tothe former's less demanding steric environment relative to the latter.This difference in steric environment is seen in the X-ray crystalstructure of compound 17, which shows two conformers: one with acoplanar ligand conformation, and another with an orthogonal one. Thislatter conformation is expected to have reduced ε_(CT) and consequentlylower k_(r). Each of compounds 11, 17, and 18 in frozen glassy media at77K exhibit an emission spectra that is narrow and long-lived, andcarbazolide-centered in nature. This is similar to what we observe withcompounds 12, 13, and 14. The mixing between the CT and ³LE manifolds inthis series of compounds appears to be strongly-dependent on the medium,a property that has been observed in other TADF systems. Furthermore, itis notable that the carbene-centered triplet in the compounds is alsowithin 1 eV from the CT/³LE manifold, and could very well play a role indetermining the excited state properties.

TABLE 3 Photophysical properties of compounds in 2-MeTHF and inMeCy^(a). λ_(max,) nm τ_(RT) λ_(max,) nm τ_(77K) Comp. RT Φ_(RT) (μs)k_(r, RT) s⁻¹ k_(nr, RT) s⁻¹ 77K (μs) 12a 492 1.0 2.3 4.4 × 10⁵ — 4307300 13 518 0.71 0.37 1.9 × 10⁶ 7.8 × 10⁵ 432 23,000 13^(a) 492 1.0 0.5 2 × 10⁶ — — — 14 502 0.95 1.2 7.9 × 10⁵ 4.2 × 10⁴ 426 508  9 580 0.270.7 3.9 × 10⁵ 1.0 × 10⁵ 498 270 15 618 0.01 0.38 2.6 × 10⁴ 2.6 × 10⁶ 50414 16 608 0.04 0.10 4.0 × 10⁵ 1.0 × 10⁷ 500 41 11^(a) 428 0.42 1.26 3.3× 10⁵ 4.6 × 10⁵ 428 6300 17^(a) 430 0.58 1.04 5.6 × 10⁵ 4.4 × 10⁵ 4326900 18^(a) 424 0.88 1.02 8.6 × 10⁵ 1.2 × 10⁵ 424 457

TABLE 4 Redox properties Comp. E_(ox) (V) E_(red) (V) E_(HOMO) (eV)E_(LUMO) (eV) 12a 0.239 −2.84 −5.06 −1.48 13 0.19 −2.8 −5.01 −1.53 140.33 −2.72 −5.17 −1.62 Electrochemical studies performed in acetonitrileversus Fc⁺/Fc. The redox peaks were taken from differential pulsevoltammograms (DPV), and converted to HOMO/LUMO energies using theequations in ref.x

The data reported in Table 5 is intended to demonstrate trends in theseries of compounds. The table data do not represent their respectiveabsolute value as calculations at this level are known to divergestrongly from experiment for compounds with strong charge transfercharacter over long range. Notably, the trends in the frontier molecularorbital energy levels match those obtained experimentally fromelectrochemical measurements: In the first CAAC series, gold compound 14has the lowest-lying HOMO and LUMO levels, which is consistent with theelectrochemical observation that it is the hardest to oxidize and theeasiest to reduce. Compound 13 is the easiest to oxidize having theshallowest HOMO, whereas compound 12 has the shallowest LUMO. This is inagreement with what is observed electrochemically, with the silvercompound 13 being the easiest to oxidize and the copper compound 12being the most difficult to reduce.

Time-dependent DFT (TDDFT) calculations also reveal trends that largelymatch experiment, with the oscillator strengths (f) of the lowest-energyCT transitions (predominantly HOMO to LUMO in character) trending in thefollowing order of increasing strength: f_(Ag)<f_(Cu)<f_(Au).Furthermore, the calculated S₁−T₁ splitting, ΔE_(S1-T1) is reproduced inthe trends observed in the increasing HOMO-LUMO separation fromCu<Au<Ag. The calculated bond lengths match the experimental onesobserved in the crystal structures. The DFT data above highlight theimportance of maintaining minimal HOMO/LUMO overlap as well as strongspin-orbit coupling by virtue of a heavy metal in order to obtainefficient TADF with sub-microsecond radiative lifetimes.

Compared with MAAC*-Cu(Cz) compound 3, corresponding gold compound 20shows a strong CT absorption at 420 nm and the molar absorptivity isabout 1.5 times higher, see FIG. 30 . The emission spectra of compound20 in polystyrene films, methylcyclohexane and 2-methylTHF (2-MeTHF) areshown in FIG. 33 and the spectra of compound 3 are shown in FIG. 31 forcomparison. The photophysical results are summarized in Table 6. Theemission profile of the Au(I) compound at room temperature is almostunchanged from that of the Cu(I) compound. The photoluminescent quantumyield is comparable to the Cu(I) compound, whereas the decay lifetime isslightly smaller. Therefore, the radiative rate constant (k_(r)) of thegold compound is higher than that of the copper compound.

The emission spectra are red-shifted from polystyrene films tomethylcyclohexane and to 2-methylTHF at room temperature due to thesolvatochromic effect. The CT excited states are stabilized uponincreasing the solvent polarity. Upon cooling to 77 K, the emissionshows a strong mixture of CT and LE character in methylcyclohexane andmethylTHF. The LE character is stronger in 2-methylTHF due to thestronger rigidochromic effect in the more polar solvent. It is worthnoting that the LE character of the emission at 77 K in bothmethylcyclohexane and 2-methylTHF is more dominant in the gold compoundthan that of the copper compound, which is due to the heavy metal effectof Au on intersystem crossing between the singlet and triplet states. At77 K, the decay lifetime of the ³LE state in 2-methylTHF decreases byalmost a factor of 10 from compound 3 (2.1 ms) to compound 20 (0.26 ms),whereas that of the ³CT state decreases only by a factor of 2 (from 181μs to 82 μs, respectively). The more dominant LE character of theemission of the gold compound at 77 K is therefore attributed toenhanced ISC due to the heavier Au nucleus.

Similar to what is observed in the CAAC- and BzI-series, theMAAC*-Ag(Cz) compound 19 shows an absorption spectrum with the weakestCT absorption band. At room temperature, emission line shapes of thesilver compound in various media are comparable to the correspondingcopper and gold compounds, with a small red-shift in fluid mediarelative to compounds 3 and 20. Upon doping into a more rigid PS matrix,non-radiative decay rate are suppressed, leading to an enhancedΦ_(PL)=0.79 and a remarkable k_(r)=2.4×10⁶ s⁻¹. This sub-microsecondexcited state lifetime is in follows the same observation with ourCAAC-Ag(Cz) compound 13, demonstrating that Ag(I) compounds are indeed aviable means to obtaining ultra-fast, tunable luminescence that utilizestriplet excitons. In addition, at 77K in PS films, where rigidochromiceffects due to matrix reorganization are largely suppressed, thecompound 19 emission is still broad and featureless, with decaylifetimes that are longer, at 7.7 μs compared to 0.33 μs at RT. This islikely due to TADF occurring within the CT manifold. The 77K decay timeof silver compound 19 is the shortest among the corresponding copper andgold compounds. These observation and data provides insight into themagnitude of ΔE_(1CT-3CT) being smallest for compound 19, and therefore,provide a highly-efficient TADF.

TABLE 6 Photophysical properties of compounds 3, 19, and 20 in differentmedia. λ_(max, RT) τ_(RT) k_(r, RT) k_(nr, RT) λ_(max, 77K) τ_(77K)Compound (nm) Φ_(RT) (μs) 10⁵ (s⁻¹) 10⁵ (s⁻¹) (nm) (μs) 20 PS film 5120.85 0.83 10 1.8 506 72 MeCy 522 0.88 1.1 8.0 1.1 456 68 MeTHF 544 0.500.79 6.3 6.3 428 430 nm: 260 μs 520 nm: 82 μs  19 PS film 512 0.79 0.3324 63 500   7.7 MeCy 548 0.22 0.12 18 65 438 430 nm: 5.0 ms (38%), 321μs (62%) 520 nm: 158 μs (84%) 2.3 ms (16%) MeTHF 568 0.056 0.036 15 260434 430 nm: 9.9 ms 520 nm: 113 μs (89%) 2.3 ms (11%) 3 PS film 506 0.901.4 6.4 0.71 502  227 MeCy 520 0.90 1.6 5.6 0.62 480  298 MeTHF 542 0.551.1 5.0 4.1 432 430 nm: 2.1 ms (62%), 342 μs (38%) 520 nm: 181 μs

We describe the making of bottom-emitting OLED devices with thetwo-coordinate Cu(I) compounds 2, 3 and 6a ((CAAC)CuCz) as dopants invarious host materials by vapor deposition. A device with Cu(I) compound6a as a dopant is to our knowledge the first device with an EML thatincludes both a Cu(I) compound host and a Cu(I) compound emitter.

A series of temperature-dependent emission spectra of a 5 wt % PMMA filmof compound 12a exhibits a change with increasing temperature. A sharpemission line at 77K is indicative of carbazole based phosphorescence.Moreover, the relatively long lifetime at 77K is indicative of anorganic triplet, as expected for a carbaozole based triplet. As thetemperature is increased from 77K a broad emission line grows in,indicative of an MLCT transition, which includes an edge at higherenergy than that of the carbazole based emission. At low temperature theexcited state is trapped in the lower energy carbazole state because thethermal energy is too low to promote the molecule into the highlyluminescent MLCT state. The marked decrease in lifetime on warming toroom temperature is consistent with efficiency emission from an MLCT dueto enhanced spin orbit coupling available to the metal compound. Themechanism of emission at room temperature is termed Thermally AssistedPhosphorescence (TAP).

The two coordinate metal(I) carbene compounds of the invention,particularly those with high excited state energies, can also be used asa host or a co-host material. For example, one can use the 2-coordinateCu(I) carbene compounds as dopants in the emissive layer of efficientOLEDs (most efficient Cu-based OLEDs employ a co-deposited EML withpolynuclear (CuX)_(n) core (n≥2) and an organic ligand).

In some embodiments, the OLED has one or more characteristics selectedfrom the group consisting of being flexible, being rollable, beingfoldable, being stretchable, and being curved. In some embodiments, theOLED is transparent or semi-transparent. In some embodiments, the OLEDfurther comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising adelayed fluorescent emitter. In some embodiments, the OLED comprises aRGB pixel arrangement or white plus color filter pixel arrangement. Insome embodiments, the OLED is a mobile device, a hand held device, or awearable device. In some embodiments, the OLED is a display panel havingless than 10 inch diagonal or 50 square inch area. In some embodiments,the OLED is a display panel having at least 10 inch diagonal or 50square inch area. In some embodiments, the OLED is a lighting panel.

According to another aspect, an emissive region in an OLED (e.g., theorganic layer described herein) is disclosed. The emissive regioncomprises a first compound as described herein. In some embodiments, thefirst compound in the emissive region is an emissive dopant or anon-emissive dopant. In some embodiments, the emissive dopant furthercomprises a host, wherein the host comprises at least one selected fromthe group consisting of metal complex, triphenylene, carbazole,dibenzothiophene, dibenzofuran, dibenzoselenophene, aza-triphenylene,aza-carbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene. In some embodiments, the emissive region furthercomprises a host, wherein the host is selected from the group consistingof:

and combinations thereof.

The organic layer can also include a host. In some embodiments, two ormore hosts are preferred. In some embodiments, the hosts used maybe a)bipolar, b) electron transporting, c) hole transporting or d) wide bandgap materials that play little role in charge transport. In someembodiments, the host can include a metal complex. The host can be atriphenylene containing benzo-fused thiophene or benzo-fused furan. Anysubstituent in the host can be an unfused substituent independentlyselected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1),OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1),C≡C—C_(n)H_(2n+1), Ar₁, Ar₁-Ar₂, and C_(n)H_(2n)-Ar₁, or the host has nosubstitutions. In the preceding substituents n can range from 1 to 10;and Ar₁ and Ar₂ can be independently selected from the group consistingof benzene, biphenyl, naphthalene, triphenylene, carbazole, andheteroaromatic analogs thereof. The host can be an inorganic compound.For example a Zn containing inorganic material e.g. ZnS.

In some embodiments, the compound can be an emissive dopant. In someembodiments, the compound can produce emissions via phosphorescence,fluorescence, thermally activated delayed fluorescence, i.e., TADF (alsoreferred to as E-type delayed fluorescence; see, e.g., U.S. applicationSer. No. 15/700,352, which is hereby incorporated by reference in itsentirety), triplet-triplet annihilation, or combinations of theseprocesses. In some embodiments, the emissive dopant can be a racemicmixture, or can be enriched in one enantiomer.

According to another aspect, a formulation comprising the compounddescribed herein is also disclosed.

The OLED disclosed herein can be incorporated into one or more of aconsumer product, an electronic component module, and a lighting panel.The organic layer can be an emissive layer and the compound can be anemissive dopant in some embodiments, while the compound can be anon-emissive dopant in other embodiments.

In yet another aspect of the present disclosure, a formulation thatcomprises the novel compound disclosed herein is described. Theformulation can include one or more components selected from the groupconsisting of a solvent, a host, a hole injection material, holetransport material, electron blocking material, hole blocking material,and an electron transport material, disclosed herein.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:EP01617493, EP01968131, EP2020694, EP2684932, US20050139810,US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455,WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804,US20150123047, and US2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but are not limited to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene; the group consistingof aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Each Ar may beunsubstituted or may be substituted by a substituent selected from thegroup consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylicacids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are notlimited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁺/Fc couple lessthan about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used inan OLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334,EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701,EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765,JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473,TW201139402, U.S. Ser. No. 06/517,957, US20020158242, US20030162053,US20050123751, US20060182993, US20060240279, US20070145888,US20070181874, US20070278938, US20080014464, US20080091025,US20080106190, US20080124572, US20080145707, US20080220265,US20080233434, US20080303417, US2008107919, US20090115320,US20090167161, US2009066235, US2011007385, US20110163302, US2011240968,US2011278551, US2012205642, US2013241401, US20140117329, US2014183517,U.S. Pat. Nos. 5,061,569, 5,639,914, WO05075451, WO07125714, WO08023550,WO08023759, WO2009145016, WO2010061824, WO2011075644, WO2012177006,WO2013018530, WO2013039073, WO2013087142, WO2013118812, WO2013120577,WO2013157367, WO2013175747, WO2014002873, WO2014015935, WO2014015937,WO2014030872, WO2014030921, WO2014034791, WO2014104514, WO2014157018.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and/or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of other organic compounds used as host are selected from thegroup consisting of aromatic hydrocarbon cyclic compounds such asbenzene, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene; the group consisting of aromatic heterocycliccompounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene,furan, thiophene, benzofuran, benzothiophene, benzoselenophene,carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine,phenothiazine, phenoxazine, benzofuropyridine, furodipyridine,benzothienopyridine, thienodipyridine, benzoselenophenopyridine, andselenophenodipyridine; and the group consisting of 2 to 10 cyclicstructural units which are groups of the same type or different typesselected from the aromatic hydrocarbon cyclic group and the aromaticheterocyclic group and are bonded to each other directly or via at leastone of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorusatom, boron atom, chain structural unit and the aliphatic cyclic group.Each option within each group may be unsubstituted or may be substitutedby a substituent selected from the group consisting of deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, and when it is aryl or heteroaryl, it has thesimilar definition as Ar's mentioned above. k is an integer from 0 to 20or 1 to 20. X¹⁰¹ to X¹⁰⁸ are independently selected from C (includingCH) or N. Z¹⁰¹ and Z¹⁰² are independently selected from NR¹⁰¹, O, or S.

Non-limiting examples of the host materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: EP2034538,EP2034538A, EP2757608, JP2007254297, KR20100079458, KR20120088644,KR20120129733, KR20130115564, TW201329200, US20030175553, US20050238919,US20060280965, US20090017330, US20090030202, US20090167162,US20090302743, US20090309488, US20100012931, US20100084966,US20100187984, US2010187984, US2012075273, US2012126221, US2013009543,US2013105787, US2013175519, US2014001446, US20140183503, US20140225088,US2014034914, U.S. Pat. No. 7,154,114, WO2001039234, WO2004093207,WO2005014551, WO2005089025, WO2006072002, WO2006114966, WO2007063754,WO2008056746, WO2009003898, WO2009021126, WO2009063833, WO2009066778,WO2009066779, WO2009086028, WO2010056066, WO2010107244, WO2011081423,WO2011081431, WO2011086863, WO2012128298, WO2012133644, WO2012133649,WO2013024872, WO2013035275, WO2013081315, WO2013191404, WO2014142472,US20170263869, US20160163995, U.S. Pat. No. 9,466,803,

Additional Emitters:

One or more additional emitter dopants may be used in conjunction withthe compound of the present disclosure. Examples of the additionalemitter dopants are not particularly limited, and any compounds may beused as long as the compounds are typically used as emitter materials.Examples of suitable emitter materials include, but are not limited to,compounds which can produce emissions via phosphorescence, fluorescence,thermally activated delayed fluorescence, i.e., TADF (also referred toas E-type delayed fluorescence), triplet-triplet annihilation, orcombinations of these processes.

Non-limiting examples of the emitter materials that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526,EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907,EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652,KR20120032054, KR20130043460, TW201332980, U.S. Ser. No. 06/699,599,U.S. Ser. No. 06/916,554, US20010019782, US20020034656, US20030068526,US20030072964, US20030138657, US20050123788, US20050244673,US2005123791, US2005260449, US20060008670, US20060065890, US20060127696,US20060134459, US20060134462, US20060202194, US20060251923,US20070034863, US20070087321, US20070103060, US20070111026,US20070190359, US20070231600, US2007034863, US2007104979, US2007104980,US2007138437, US2007224450, US2007278936, US20080020237, US20080233410,US20080261076, US20080297033, US200805851, US2008161567, US2008210930,US20090039776, US20090108737, US20090115322, US20090179555,US2009085476, US2009104472, US20100090591, US20100148663, US20100244004,US20100295032, US2010102716, US2010105902, US2010244004, US2010270916,US20110057559, US20110108822, US20110204333, US2011215710, US2011227049,US2011285275, US2012292601, US20130146848, US2013033172, US2013165653,US2013181190, US2013334521, US20140246656, US2014103305, U.S. Pat. Nos.6,303,238, 6,413,656, 6,653,654, 6,670,645, 6,687,266, 6,835,469,6,921,915, 7,279,704, 7,332,232, 7,378,162, 7,534,505, 7,675,228,7,728,137, 7,740,957, 7,759,489, 7,951,947, U.S. Pat. Nos. 8,067,099,8,592,586, 8,871,361, WO06081973, WO06121811, WO07018067, WO07108362,WO07115970, WO07115981, WO08035571, WO2002015645, WO2003040257,WO2005019373, WO2006056418, WO2008054584, WO2008078800, WO2008096609,WO2008101842, WO2009000673, WO2009050281, WO2009100991, WO2010028151,WO2010054731, WO2010086089, WO2010118029, WO2011044988, WO2011051404,WO2011107491, WO2012020327, WO2012163471, WO2013094620, WO2013107487,WO2013174471, WO2014007565, WO2014008982, WO2014023377, WO2014024131,WO2014031977, WO2014038456, WO2014112450.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and/or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, when it is aryl or heteroaryl, it has the similardefinition as Ar's mentioned above. Ar¹ to Ar³ has the similardefinition as Ar's mentioned above. k is an integer from 1 to 20. X¹⁰¹to X¹⁰⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms 0, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

Non-limiting examples of the ETL materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: CN103508940,EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918,JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977,US2007018155, US20090101870, US20090115316, US20090140637,US20090179554, US2009218940, US2010108990, US2011156017, US2011210320,US2012193612, US2012214993, US2014014925, US2014014927, US20140284580,U.S. Pat. Nos. 6,656,612, 8,415,031, WO2003060956, WO2007111263,WO2009148269, WO2010067894, WO2010072300, WO2011074770, WO2011105373,WO2013079217, WO2013145667, WO2013180376, WO2014104499, WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. may be undeuterated, partially deuterated, andfully deuterated versions thereof. Similarly, classes of substituentssuch as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc.also may be undeuterated, partially deuterated, and fully deuteratedversions thereof.

EXPERIMENTAL 1. Synthesis of (MAAC*)CuCl (1a).

3-Chloro-N-(2,6-diisopropylphenyl)-N′-((2,6-diisopropylphenylimino)methyl)-2,2-dimethylpropanamide(1c). N,N′-bis(2,6-diisopropylphenyl) formamidine (500 mg, 1.37 mmol)and triethylamine (287 mL, 2.06 mmol) were dissolved in dichloromethane(20 mL) and stirred at 0° C. for 10 min, after which 3-chloropivaloylchloride (0.195 mL, 1.51 mmol) was added dropwise. The solution mixturewas stirred for 3 h at 0° C. The solvent was removed under reducedpressure to afford a white powder, which was extracted with toluene andfiltered through Celite. Removal of the residual solvent afforded theproduct as a white solid. Yield: 650 mg (98%).

1,3-bis(2,6-diisopropylphenyl)-5,5-dimethyl-4-keto-tetrahydropyrimidin-1-iumchloride (1b). 1c (650 mg, 1.34 mmol) was dissolved in toluene (20 mL)and the solution was refluxed for 16 h at 110° C. during which a whiteprecipitate formed. The reaction mixture was cooled to RT and the whiteprecipitate was collected by vacuum filtration and washed with coldtoluene. Yield: 450 mg (69%).

(N,N′-bis(diisopropylphenyl)-5,5-dimethyl-4-keto-tetrahydropyrimidin-2-ylidene)-Cu(I)chloride (MAAC*CuCl) (1a). KHMDS (136 mg, 0.68 mmol) was added to a THFsolution (20 mL) of 1b (300 mg, 0.62 mmol) at RT and the solution wasstirred for 1 h before CuCl (67 mg, 0.68 mmol) was added. The reactionmixture was stirred at RT for 16 h, filtered through Celite and thesolvent was concentrated to 3 mL under reduced pressure. Hexane (20 mL)was added to the solution and a white precipitate formed. Yield: 300 mg(88%).

2. Synthesis of [(DAC*)Cu]₂Cl₂ (2a).

KHMDS (450 mg, 2.28 mmol) was added to a THF solution (20 mL) of 2b(1.39 g, 2.28 mmol) at RT and the solution was stirred for 1 h beforeCuCl (230 mg, 2.28 mmol) was added. The reaction mixture was stirred atRT for 16 h. The solvent was evaporated under reduced pressure, and theobtained red solid was re-dissolved in toluene (20 mL) and filteredthrough Celite. The filtrate was concentrated to 3 mL under reducedpressure. Hexane (20 mL) was added to the solution and a red precipitateformed. Yield: 400 mg (31%).

3. Synthesis of Compounds 1-5

General procedure. Carbazole ligand and NaOtBu were dissolved in THF andstirred for 3 h at RT. (carbene)CuCl was added to the reaction mixtureand stirred for 16 h. The resulting mixture was filtered through Celiteand the solvent was removed under reduced pressure to afford a solid.The solid was re-dissolved in dichloromethane and hexane was added toprecipitate out the desired product.

(MAAC*)Cu(CzCN₂) (1). The compound was made from (MAAC*)CuCl (160 mg,0.29 mmol), CzCN₂ (64 mg, 0.29 mmol) and NaO^(t)Bu (29 mg, 0.30 mmol) asa white solid. Yield: 168 mg (85%).(MAAC*)Cu(CzCN) (2). The compound was made from (MAAC*)CuCl (200 mg,0.37 mmol), CzCN (71 mg, 0.37 mmol) and NaO^(t)Bu (36 mg, 0.37 mmol) asa white solid. Yield: 200 mg (78%).(MAAC*)Cu(Cz) (3). The compound was made from (MAAC*)CuCl (2.0 g, 3.67mmol), Cz (613 mg, 3.67 mmol) and NaO^(t)Bu (353 mg, 3.67 mmol) as ayellow solid. Yield: 2.1 g (85%).(DAC*)Cu(CzCN) (4). The compound was made from (DAC*)CuCl (200 mg, 0.36mmol), CzCN (69 mg, 0.36 mmol) and NaO^(t)Bu (35 mg, 0.36 mmol) as anorange solid. Yield: 200 mg (76%).(DAC*)Cu(Cz) (5). The compound was made from (DAC*)CuCl (100 mg, 0.18mmol), Cz (30 mg, 0.18 mmol) and NaO^(t)Bu (18 mg, 0.19 mmol) as apurple solid. The compound was extremely air-sensitive.(CAAC^(Men)Cu(NPh₂) (9). The compound was made from (CAAC^(Men))CuCl(950 mg, 1.98 mmol), HNPh₂ (351 mg, 2.08 mmol) and NaO^(t)Bu (200 mg,2.08 mmol) as a bright yellow solid. Yield: 1.1 g (93%). The compound isexceedingly sensitive to moisture, especially in solution.(CAAC^(Ad)Cu(Me₂Cz) (10b). The compound was made from (CAAC^(Ad))CuCl(250 mg, 0.52 mmol), Me₂Cz (109 mg, 0.52 mmol) and KO^(t)Bu (59 mg, 0.53mmol) as a pale yellow solid. The solid was washed with ether, extractedwith toluene, then washed with pentane. Yield: 311 mg (93%). Thecompound is exceedingly sensitive to moisture, especially in solution.(BzI-Cu(Cz) (11). The compound was made from (BzI)CuCl (120 mg, 0.22mmol), Cz (39 mg, 0.23 mmol) and NaO^(t)Bu (23 mg, 0.23 mmol) as a whitesolid. Yield: 135 mg (90.5%).

Scheme

A-D: CAAC E: Bzl carbene NR₂ 6a A Cz (R₁, R₂ = H) 6b B Cz (R₁, R₂ = H)6c C Cz (R₁, R₂ = H) 6d D Cz (R_(1,) R₂ = H) 10b B Cz (R₁ = H, R₂ = Me)7 A Cz (R₁ = CN, R₂ = H) 8 A Cz (R₁ = OMe, R₂ = H) 9 A NPh₂ 11 E Cz (R₁,R₂ = H)

(MAAC*)CuCz (3) Based Green OLED Devices

Devices 1 and 2. Device 1 is fabricated using HATCN as hole injectinglayer (HIL) and NPD as hole-transporting layer (HTL), FIG. 15 a . Theemissive layer (EML) includes 10 wt. % of compound 3 doped in mCBP host.Bphen was used for hole-blocking (HBL) and electron transporting (ETL).Device 2 has a similar structure as device 1 except that the holeinjecting layer, HATCN, is absent. The electroluminescence spectra areconsistent with the photoluminescent spectra, FIG. 16 . The maximumexternal quantum efficiency (EQE) of the two devices are −6% even thoughthe internal quantum efficiency is 100%. This is likely due to the lowertriplet energy of NPD (2.30 eV) than that of the dopant (2.75 eV).Therefore, HTL with higher triplet energy or exciton blocking layerbetween HTL and EML is needed to prevent exciton leaking into HTL.

Device 3. mCP (E_(T)=2.90 eV) is used as an exciton blocking layerbetween HTL and EML, FIG. 17 a . There is an extra peak in the EL at˜420 nm which is attributed to NPD emission, FIG. 17 b . This occurreddue to the deep HOMO (6.0 eV) of mCP that slowed down thehole-transporting rate which leads to charge recombination in NPD layer.

Device 4. High-triplet material TAPC (E_(T)=2.87 eV) was used as HTL,FIG. 18 a . The EQE is 8.1%, which is higher that with NPD as HTL(devices 1 and 2). The electroluminescence comes exclusively from thedopant, FIG. 18 b.

Devices 5, 6 and 7. High triplet material TPBi (ET=2.73 eV) was used asHBL instead of Bphen (E_(T)=2.50 eV), FIG. 19 a . The EQE of the TPBidevice (D5) turned out to be very similar to that of the Bphen device(D4) with the same doping concentration, FIG. 19 b . In addition, theEQE was not changing as the doping concentration was increased to 20%and 40%, FIG. 20 . Therefore, 10% doping concentration will be used forthe following devices.

Devices 8, 9 and 10. mCP was used as an exciton blocking layer. The ETLthickness varied from 30 nm, 40 nm to 50 nm, FIG. 21 a . D9 and D5 showsimilar EQE (same ETL thickness), which indicates that mCP layer was notnecessary. As the ETL thickness increases from 30 nm to 50 nm, the EQEincreases from 8% to 10%, FIG. 21 b . Therefore, 50 nm is the optimumETL thickness to get efficient light outcoupling.

(MAAC*)Cu(CzCN) (2) Based Blue OLED Devices

The triplet of (MAAC*)Cu(CzCN) is 3.1 eV (onset) which is much higherthan that of mCBP (2.87

TABLE 7 Turn-on voltage (V_(T), defined at brightness of 1 cd/m²),maximum external quantum efficiency (EQE_(max)), maximum currentefficiency (η_(c,max)), maximum power efficiency (η_(p,max)), maximumbrightness (B_(max)), and emission maximum (λ_(max)) of the OLEDs withdifferent dopants. EQE_(max) η_(c,max) η_(p,max) B_(max) λ_(max) DopantDevice V_(T) (V) (%) (cd/A) (lm/W) (cd/m²) (nm) 3 1 3.3 6.1 18.5 15.227600 510 2 3.3 5.5 17.0 14.5 25217 518 3 3.1 9.3 24.8 21.5 23527 500 42.6 8.1 24.9 23.9 43304 508 5 2.5 8.1 23.4 27.5 31800 508 6 2.5 7.6 22.427.0 31715 510 7 2.4 7.5 23.0 28.8 33643 512 8 2.8 6.0 16.3 17.5 26916500 9 2.8 8.1 23.6 25.8 31597 506 10 2.8 10.2 29.1 31.7 36911 502 2 112.8 1.1 1.9 1.7 1077 466  6a 12 3.5 5.8 10.9 7.8 466 456eV). Therefore, the EQE is only about 1%. High triplet host material isneeded.

Compound 9

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-CuCl (950 mg, 1.98 mmol); diphenylamine (351 mg, 2.1 mmol);NaOtBu (199 mg, 2.1 mmol) under N₂ atmosphere. THF was added and thereaction mixture was stirred at room temperature overnight. The mixturewas then filtered through a plug of Celite® and the solvent wasevaporated under reduced pressure. The resulting bright yellow powderwas washed with pentane and dried under vacuum. 1.12 mg, 96% yield.

Compound 11

A round bottom flask equipped with a stir bar was charged with BzI-CuCl(120 mg, 0.22 mmol); carbazole (39 mg, 0.23 mmol); NaOtBu (22 mg, 0.23mmol) under N₂ atmosphere. THF was added and the reaction mixture wasstirred at room temperature overnight. The mixture was then filteredthrough a plug of Celite® and the solvent was evaporated under reducedpressure. The resulting grey solid was washed with pentane and driedunder vacuum. 135 mg, 90.5% yield.

Compound 12a

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-CuCl (200 mg, 0.42 mmol); carbazole (73 mg, 0.44 mmol);NaOtBu (42 mg, 0.44 mmol) under N₂ atmosphere. THF was added and thereaction mixture was stirred at room temperature overnight. The mixturewas then filtered through a plug of Celite® and the solvent wasevaporated under reduced pressure. The resulting pale yellow solid waswashed with pentane and dried under vacuum. 228 mg, 90% yield.

Compounds 12b, 12c, and 12d

Compounds 12b, 12c, and 12d were also prepared as described for compound12a with the corresponding substituted carbazoles indicated below, andthe carbene ligand of compound 12a.

FIG. 22 is the emission spectra of compounds 12a (labeled 4), compound12c (labeled 6), and compound 12d (labeled 7) in MeCy at roomtemperature.

Compound 13

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-AgCl (100 mg, 0.19 mmol); carbazole (33 mg, 0.2 mmol); NaOtBu(19 mg, 0.2 mmol) under N₂ atmosphere. THF was added and the reactionmixture was stirred at room temperature overnight. The mixture was thenfiltered through a plug of Celite® and the solvent was evaporated underreduced pressure. The resulting white solid was washed with pentane anddried under vacuum. 120 mg, 96% yield.

Compound 14

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-AuCl (100 mg, 0.16 mmol); carbazole (28 mg, 0.17 mmol);NaOtBu (16 mg, 0.17 mmol) under N₂ atmosphere. THF was added and thereaction mixture was stirred at room temperature overnight. The mixturewas then filtered through a plug of Celite® and the solvent wasevaporated under reduced pressure. The resulting greyish-white solid waswashed with pentane and dried under vacuum. 128 mg, >100% yield, due toexcess Cz.

FIG. 23 is the emission spectra of compounds 12 (spectrum 1), compound13 (spectrum 2), and compound 14 (spectrum 3) at THF, 77K (left), and inMeTHF, RT (right) RT. FIG. 24 is the absorption and emission spectra ofcompound 12 in MeCy (dashed lines) and 2-MeTHF (solid lines) at RT.

Compound 15

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-AgCl (200 mg, 0.38 mmol); diphenylamine (68 mg, 0.4 mmol);NaOtBu (38 mg, 0.4 mmol) under N₂ atmosphere. THF was added and thereaction mixture was stirred at room temperature overnight. The mixturewas then filtered through a plug of Celite® and the solvent wasevaporated under reduced pressure. The resulting pale yellow solid waswashed with pentane and dried under vacuum. 194 mg, 77% yield.

Compound 16

A round bottom flask equipped with a stir bar was charged withCAAC^(Men)-AuCl (200 mg, 0.32 mmol); diphenylamine (58 mg, 0.34 mmol);NaOtBu (33 mg, 0.34 mmol) under N₂ atmosphere. THF was added and thereaction mixture was stirred at room temperature overnight. The mixturewas then filtered through a plug of Celite® and the solvent wasevaporated under reduced pressure. The resulting bright yellow solid waswashed with pentane and dried under vacuum. 180 mg, 74% yield.

FIG. 25 is the emission spectra in THF (left), and in 2-MeTHF (right),of compound 9 (spectrum 4), compound 15 (spectrum 5), and compound 16(spectrum 6), at room temperature and 77K.

Compound 17

A round bottom flask equipped with a stir bar was charged with BzI-AgCl(150 mg, 0.26 mmol); carbazole (47 mg, 0.28 mmol); NaOtBu (27 mg, 0.28mmol) under N₂ atmosphere. THF was added and the reaction mixture wasstirred at room temperature overnight. The mixture was then filteredthrough a plug of Celite® and the solvent was evaporated under reducedpressure. The resulting grey solid was washed with pentane and driedunder vacuum. 130 mg, 71% yield.

Compound 18

A round bottom flask equipped with a stir bar was charged with BzI-AuCl(120 mg, 0.18 mmol); carbazole (33 mg, 0.2 mmol); NaOtBu (19 mg, 0.2mmol) under N₂ atmosphere. THF was added and the reaction mixture wasstirred at room temperature overnight. The mixture was then filteredthrough a plug of Celite® and the solvent was evaporated under reducedpressure. The resulting grey solid was washed with pentane and driedunder vacuum. 116 mg, 81% yield.

FIG. 26 is the absorption and emission spectra of compound 11 (spectrum7), compound 17 (spectrum 8), and compound 18 (spectrum 9) in MeCy atroom temperature.

Compound 19

(MAAC*)Ag(Cz) (11). MAAC*AgCl (100 mg, 0.17 mmol) and KCz (35 mg, 0.17mmol) were dissolved in THF (20 mL) and the reaction mixture was stirredat RT overnight, filtered through Celite and the solvent wasconcentrated to 3 mL under reduced pressure. Hexane (20 mL) was added tothe solution and a yellow precipitate formed. The solid was dried undervacuum.

FIG. 27 is the emission spectra of compound 3 at room temperature and at77K in 2-MeTHF, MeCy, and as 1% PS film. FIG. 28 is the emission spectraof compound 19 at room temperature and at 77K in 2-MeTHF, MeCy, and as1% PS film.

Compound 20

Compound 21

A round bottom flask equipped with a stir bar was charged with pzl-CuCl(54 mg, 0.126 mmol); carbazole (22 mg, 0.133 mmol); and NaOtBu (13 mg,0.133 mmol) under N₂ atmosphere. THF was added and the reaction mixturewas stirred at room temperature overnight. The mixture was then filteredthrough a plug of Celite® and the solvent was evaporated under reducedpressure. The resulting bright yellow solid was washed with pentane anddried under vacuum. 50 mg, 71% yield.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A compound having Formula I

wherein ring A and ring B are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic; together with nitrogen atoms bonded to ring A andring B, ring W is a 5-membered N-heterocyclic carbene; L is amonodentate ligand with a coordinating member selected from the groupconsisting of C, N, O, S, and P; M is a metal selected from the groupconsisting of Cu, Au, and Ag; R^(A), R^(B), and R^(W) represent mono tothe maximum allowable substitution, or no substitution, and each R^(A)and R^(B) is independently selected from the group consisting ofhydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, nitrile,isonitrile, sulfanyl, and combinations thereof; R^(W) is selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof; or optionally, any two adjacent R^(A), R^(B), orR^(W) can join to form a ring, which is optionally substituted; and twoR^(W) do not join to form a naphthalene fused to ring W.
 2. The compoundof claim 1, wherein ring W is an N-heterocyclic carbene derived from achemical group selected from the group consisting of imidazolidine,imidazole, triazolidine, and triazole.
 3. The compound of claim 1,wherein L is selected from the group consisting of: NR^(X)R^(Y),PR^(X)R^(Y), CR^(X)R^(Y)R^(Z), substituted phenyl, OR^(X), and SR^(X),wherein R^(X), R^(Y), and R^(Z) are independently selected from thegroup consisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, aryl, heteroaryl, and combinations thereof; each ofwhich is optionally substituted, or optionally, R^(X) and R^(Y) can jointo form five-membered or six-membered, carbocyclic or heterocyclic ring,which is optionally substituted.
 4. The compound of claim 1, whereinring B is selected from the group consisting of: an optionallysubstituted cycloalkyl with 5 to 10 carbons; an optionally substitutedaryl with 6 to 10 carbons; an optionally substituted heterocyclic with 3to 8 carbons and 1 to 3 heteroatoms; and an optionally substitutedheteroaryl with 3 to 8 carbons and 1 to 4 heteroatoms.
 5. The compoundof claim 3, wherein L is NR^(X)R^(Y) and is selected from the groupconsisting of: an optionally substituted carbazoyl, or an aza-derivativethereof; an optionally substituted diphenylamino, or an aza-derivativethereof;


6. The compound of claim 3, wherein R^(X) and/or R^(Y) is selected fromthe group consisting of: an aryl optionally substituted with deuterium,alkyl, or an electron donating substituent group; a heteroaryloptionally substituted with deuterium, alkyl, or an electron donatingsubstituent group; and an alkyl optionally substituted with one or moredeuterium atoms.
 7. The compound of claim 1, with an emission lifetimeselected from the group consisting of 0.05 μs to 10 μs, and 0.05 μs to 2μs, as measured as a polystyrene film at 23° C.
 8. The compound of claim1, whose energy separation (ΔE) of the lowest excited singlet state andtriplet states is from 10 meV and 150 meV as determined by temperaturedependent emission lifetime measurement.
 9. The compound of claim 1,with an emission wavelength of from 450 nm to 530 nm as measured as apolystyrene film at 23° C.
 10. The compound of claim 1, with an emissionwavelength of from 530 nm to 650 nm as measured as a polystyrene film at23° C.
 11. The compound of claim 1, being an E-type delayed fluorescentemitter.
 12. The compound of claim 1, wherein the metal is Cu.
 13. Thecompound of claim 1, wherein the metal is Ag.
 14. The compound of claim1, wherein the metal is Au.
 15. The compound of claim 1, selected fromthe group consisting of:


16. An organic electroluminescent device (OLED) that includes an anode,a cathode, and an organic layer comprising a compound having Formula I

wherein ring A and ring B are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic; together with nitrogen atoms bonded to ring A andring B, ring W is a 5-membered N-heterocyclic carbene; L is amonodentate ligand with a coordinating member selected from the groupconsisting of C, N, O, S, and P; M is a metal selected from the groupconsisting of Cu, Au, and Ag; R^(A), R^(B), and R^(W) represent mono tothe maximum allowable substitution, or no substitution, and each R^(A)and R^(B) is independently selected from the group consisting ofhydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, nitrile,isonitrile, sulfanyl, and combinations thereof; R^(W) is selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof; or optionally, any two adjacent R^(A), R^(B), orR^(W) can join to form a ring, which is optionally substituted; and twoR^(W) do not join to form a naphthalene fused to ring W.
 17. The OLED ofclaim 16, wherein the device emits a luminescent radiation at roomtemperature when a voltage is applied across the organic light emittingdevice, and the luminescent radiation comprises a first radiationcomponent that arises from a delayed fluorescent process or tripletexciton harvesting process.
 18. The OLED of claim 16, wherein theorganic layer further comprises a host, wherein the host comprises atleast one chemical group selected from the group consisting oftriphenylene, carbazole, dibenzothiphene, dibenzofuran,dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene,aza-dibenzofuran, and aza-dibenzoselenophene.
 19. The OLED of claim 18,wherein the host is selected from the group consisting of:

and combinations thereof.
 20. A consumer product comprising an organiclight-emitting device (OLED), the OLED including an anode, a cathode,and an organic layer comprising A compound having Formula I

wherein ring A and ring B are independently a five-membered orsix-membered, carbocyclic or heterocyclic ring, each of which isoptionally aromatic; together with nitrogen atoms bonded to ring A andring B, ring W is a 5-membered N-heterocyclic carbene; L is amonodentate ligand with a coordinating member selected from the groupconsisting of C, N, O, S, and P; M is a metal selected from the groupconsisting of Cu, Au, and Ag; R^(A), R^(B), and R^(W) represent mono tothe maximum allowable substitution, or no substitution, and each R^(A)and R^(B) is independently selected from the group consisting ofhydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, nitrile,isonitrile, sulfanyl, and combinations thereof; R^(W) is selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof; or optionally, any two adjacent R^(A), R^(B), orR^(W) can join to form a ring, which is optionally substituted; and twoR^(W) do not join to form a naphthalene fused to ring W.